DOCSLIB.ORG

The Dawn of Physiological Closed-Loop Ventilation—A Review Philip Von Platen1* , Anake Pomprapa1, Burkhard Lachmann2 and Steffen Leonhardt1

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Dawn of Physiological Closed-Loop Ventilation—A Review Philip Von Platen1* , Anake Pomprapa1, Burkhard Lachmann2 and Steffen Leonhardt1 von Platen et al. Critical Care (2020) 24:121 https://doi.org/10.1186/s13054-020-2810-1 REVIEW Open Access The dawn of physiological closed-loop ventilation—a review Philip von Platen1* , Anake Pomprapa1, Burkhard Lachmann2 and Steffen Leonhardt1 Abstract The level of automation in mechanical ventilation has been steadily increasing over the last few decades. There has recently been renewed interest in physiological closed-loop control of ventilation. The development of these systems has followed a similar path to that of manual clinical ventilation, starting with ensuring optimal gas exchange and shifting to the prevention of ventilator-induced lung injury. Systems currently aim to encompass both aspects, and early commercial systems are appearing. These developments remain unknown to many clinicians and, hence, limit their adoption into the clinical environment. This review shows the evolution of the physiological closed-loop control of mechanical ventilation. Keywords: Closed-loop ventilation, Patient-in-the-loop, Physiological control Introduction Regulating a physiological variable of the patient is Closed-loop systems are designed to dynamically regu- known as physiological closed-loop control (PCLC). With late a given variable around a desired set point. Examples the extensive physiological monitoring in today’s clinical thereof surround our everyday lives, from cruise-control environment, PCLC is becoming ever more popular. In maintaining the correct speed on the highway, to auto- this case, the patient is the focus of the control loop and pilot flying modern airplanes safely. a physiological measurement is fed back to the controller. Modern medical systems are increasingly incorporat- The PCLC has recently been taken up by regulatory bod- ing these technological advances. Medical applications of ies, with an international standard developed specifically closed-loop control can be divided into systems that con- for it, namely the IEC 60601-1-10 [2] and a public work- trol a physical variable of the medical device and those shop held by the Food and Drug Administration in 2015 that control a physiological variable of the patient [1]. with subsequent publication by Parvinian and colleagues Many medical devices already incorporate device-internal in 2018 [3]. closed-loop control systems. An example is the inter- Importantly, PCLC allows for the automation of certain nal regulation of the fraction of inspired oxygen to the therapeutic tasks currently performed by medical staff. value set by the clinician. If there is some backward inter- Critical and emergency care especially is presumed to action between the patient and the medical device, the benefit from increased automation, as these high-stress system can be said to be patient-oriented.Thecontrolof environments have a shrinking workforce, as projected airway pressure during pressure-controlled ventilation is by Angus et al. [4]. This limited supply of medical staff, such an example, because there is interaction between the coupled with the labor-intensive practice of setting a ven- device and patient. Here, the controller also focuses on the tilator correctly [5, 6] means that proper, personalized medical device. patient care will become even more difficult in the future. The already high costs of keeping patients on mechanical *Correspondence: [email protected] ventilation [7, 8] will also increase even further. If some 1Medical Information Technology, Helmholtz-Institute for Biomedical Engineering, RWTH Aachen University, Pauwelsstr. 20, 52074 Aachen, Germany ventilator settings are adjusted automatically, this would Full list of author information is available at the end of the article increase the time and capacity of the medical staff. © The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/)appliestothedatamade available in this article, unless otherwise stated in a credit line to the data. von Platen et al. Critical Care (2020) 24:121 Page 2 of 11 Despite regaining attention recently, PCLC of mechan- covered elsewhere, (e.g., Chatbrun et al. [14]). In addition, ical ventilation has been around for over half a century. other methods of ventilation, such as liquid, noisy, and Similar to the guidelines of mechanical ventilation which high-frequency ventilation, are beyond the scope of this have evolved over time, from focusing on optimal gas paper. exchange to reducing ventilator-induced lung injury [9], a similar trend can be seen in the research into PCLC Concept of physiological closed-loop ventilation for mechanical ventilation. This review aims to show the The primary goal of mechanical ventilation is to rectify evolution of the PCLC of mechanical ventilation and its and maintain adequate gas exchange. Ventilating patients close relationship with the clinical goals of mechanical protectively has become another important goal during ventilation. mechanical ventilation. The current clinical practice for choosing ventilator set- Scope and definitions tings is very complex and based on expert knowledge. The The criteria of search for this paper was as follows. modern clinician relies on classical physiologic variables Firstly, relevant literature was identified from database for mechanical ventilation, such as peripheral capillary search combinations of the keywords: closed-loop, con- oxygen saturation (SpO2), end-tidal CO2 (etCO2), and trol, feedback and automation in combination with ven- blood gas analysis (PaO2,PaCO2, pH). In addition, clin- tilation, mechanical ventilation, and artificial ventilation. icians consider the protective guidelines, hemodynamic Secondly, the search was narrowed down to include only parameters (heart rate, blood pressure, perfusion), and systems which used patient-specific physiological vari- derived variables such as the pF ratio, the oxygen A-a gra- ables for the feedback control. The physiological variables dient, shunt, transpulmonary pressure, and mechanical can be grouped loosely into oxygen, carbon dioxide, respi- power, among others [9]. ratory mechanics, and patient demand. Thirdly, the phase The interaction of clinician, ventilator, and patient of weaning has so far benefited most from automation forms a manual closed-loop system or “clinician-in-the- and was therefore added as an additional search keyword. loop” system. This is shown in a block diagram in Fig. 1. Finally, only literature including studies with patients or Here the clinician acts as the controller and compares medium/large animals was included. Extensive additional the available physiological and derived measurements to literature on theoretical approaches and simulative results a defined control target before deciding on appropriate exists, but these still need to be validated experimentally. ventilator settings (actuation). Furthermore, previous reviews on closed-loop mechan- This clinician-in-the-loop system is labor-intensive and ical ventilation exist and provided further relevant liter- time-consuming, as the presence of the clinician is always ature. Brunner presented an important early manuscript necessary. The clinician’s full attention is required to describing the history and principles of closed-loop ven- adjust ventilator settings if the patient state changes and tilation [10]. Reviews of advanced closed-loop control in to accommodate new therapeutic needs. If the clinician mechanical ventilation have been provided by Lellouche is not present, the system becomes an open-loop system, et al. [11], Wysocki et al. [12], and Branson [13]. which is unable to respond if the oxygenation or ventila- In order to present a precise review, ventilation modes tion become insufficient due to worsening patient condi- and breathing patterns are not discussed; these have been tions or external disturbances. This may lead to the patient Fig. 1 Classical clinician-in-the-loop system. The physiological measurement and ventilator settings shown are only exemplary. In the clinical environment, further derived measurement variables are also used. Clinician refers to the physicians, respiratory therapists, or nurses von Platen et al. Critical Care (2020) 24:121 Page 3 of 11 being poorly and not protectively ventilated, with possible The evolution of automated physiological control can dire consequences. be categorized by two drivers: the control target and the controller design. The control target is dictated on the Characteristics of closed-loop ventilation one hand by the measurements and sensors available, An automated closed-loop system (also known as feed- some of which have been described above. On the other back control) can be implemented to
Load more

Recommended publications
  • Human Physiology an Integrated Approach
    Gas Exchange and Transport Gas Exchange in the Lungs and Tissues 18 Lower Alveolar P Decreases Oxygen Uptake O2 Diff usion Problems Cause Hypoxia Gas Solubility Aff ects Diff usion Gas Transport in the Blood Hemoglobin Binds to Oxygen Oxygen Binding Obeys the Law of Mass Action Hemoglobin Transports Most Oxygen to the Tissues P Determines Oxygen-Hb Binding O2 Oxygen Binding Is Expressed As a Percentage Several Factors Aff ect Oxygen-Hb Binding Carbon Dioxide Is Transported in Three Ways Regulation of Ventilation Neurons in the Medulla Control Breathing Carbon Dioxide, Oxygen, and pH Infl uence Ventilation Protective Refl exes Guard the Lungs Higher Brain Centers Aff ect Patterns of Ventilation The successful ascent of Everest without supplementary oxygen is one of the great sagas of the 20th century. — John B. West, Climbing with O’s , NOVA Online (www.pbs.org) Background Basics Exchange epithelia pH and buff ers Law of mass action Cerebrospinal fl uid Simple diff usion Autonomic and somatic motor neurons Structure of the brain stem Red blood cells and Giant liposomes hemoglobin of pulmonary Blood-brain barrier surfactant (40X) From Chapter 18 of Human Physiology: An Integrated Approach, Sixth Edition. Dee Unglaub Silverthorn. Copyright © 2013 by Pearson Education, Inc. All rights reserved. 633 Gas Exchange and Transport he book Into Thin Air by Jon Krakauer chronicles an ill- RUNNING PROBLEM fated trek to the top of Mt. Everest. To reach the summit of Mt. Everest, climbers must pass through the “death zone” T High Altitude located at about 8000 meters (over 26,000 ft ). Of the thousands of people who have attempted the summit, only about 2000 have been In 1981 a group of 20 physiologists, physicians, and successful, and more than 185 have died.
    [Show full text]
  • Physiologic Effects of Noninvasive Ventilation
    Physiologic Effects of Noninvasive Ventilation Neil R MacIntyre Introduction NIV Can Augment Minute Ventilation NIV Unloads Ventilatory Muscles NIV Resets the Ventilatory Control System Alveolar Recruitment and Gas Exchange Other Physiologic Effects of NIV: Intended and Unintended Maintaining Upper-Airway Patency Reducing Imposed Triggering Loads From Auto-PEEP Cardiac Interactions: Both Beneficial and Harmful Ventilator-Induced Lung Injury Production of Auto-PEEP Patient-Ventilator Interactions Summary Noninvasive ventilation (NIV) has a number of physiologic effects similar to invasive ventilation. The major effects are to augment minute ventilation and reduce muscle loading. These effects, in turn, can have profound effects on the patient’s ventilator control system, both acutely and chron- ically. Because NIV can be supplied with PEEP, the maintenance of alveolar recruitment is also made possible and the triggering load imposed by auto-PEEP can be reduced. NIV (or simply mask CPAP) can maintain upper-airway patency during sleep in patients with obstructive sleep apnea. NIV can have multiple effects on cardiac function. By reducing venous return, it can help in patients with heart failure or fluid overload, but it can compromise cardiac output in others. NIV can also increase right ventricular afterload or function to reduce left ventricular afterload. Potential det- rimental physiologic effects of NIV are ventilator-induced lung injury, auto-PEEP development, and discomfort/muscle overload from poor patient–ventilator interactions. Key words: invasive ventilation; noninvasive ventilation; minute and alveolar ventilation; ventilation distribution; ventilation-perfusion match- ing; control of ventilation; ventilatory muscles; work of breathing; patient–ventilator interactions; ventilator- induced lung injury. [Respir Care 2019;64(6):617–628.
    [Show full text]
  • Control of Respiration Central Control of Ventilation
    Control of Respiration Control of Respiration Bioengineering 6000 CV Physiology Central Control of Ventilation • Goal: maintain sufficient ventilation with minimal energy – Ventilation should match perfusion • Process steps: – Ventilation mechanics + aerodynamics • Points of Regulation – Breathing rate and depth, coughing, swallowing, breath holding – Musculature: very precise control • Sensors: – Chemoreceptors: central and peripheral – Stretch receptors in the lungs, bronchi, and bronchioles • Feedback: – Nerves – Central processor: • Pattern generator of breathing depth/amplitude • Rhythm generator for breathing rate Control of Respiration Bioengineering 6000 CV Physiology Peripheral Chemosensors • Carotid and Aortic bodies • Sensitive to PO2, PsCO2, and pH (CO2 sensitivity may originate in pH) • Responses are coupled • Adapt to CO2 levels • All O2 sensing is here! • Carotid body sensors more sensitive than aortic bodies Control of Respiration Bioengineering 6000 CV Physiology O2 Sensor Details • Glomus cells • K-channel with O2 sensor • O2 opens channel and hyperpolarizes cell • Drop in O2 causes reduction in K current and a depolarization • Resulting Ca2+ influx triggers release of dopamine • Dopamine initiates action potentials in sensory nerve Control of Respiration Bioengineering 6000 CV Physiology Central CO2/pH Chemoreceptors • Sensitive to pH in CSF • CSF poorly buffered • H+ passes poorly through BBB but CO2 passes easily • Blood pH transmitted via CO2 to CSF • Adapt to elevated CO2 levels (reduced pH) by transfer of - - HCO3
    [Show full text]
  • The Chemoreflex Control of Breathing and Its Measurement
    933 Continuing Medical Education The chemoreflex control of breathing James Duffin PhD and measurement The chemoreflex control of breathing is described in terms of a Le contrrle chimiorEflexe de la respiration est dEcrit comme un graphical model. The central chemoreflex, the ventilatory modEle graphique. Le centre chimiordflexe, #1 rEponse respira- response to carbon dioxide mediated by the central chemorecep- toire au C02 mEdiEe par les chEmorEcepteurs centrmLr sont tors, is modelled as a straight-line relation between the dEcrits comme une relation directe entre la rEponse respira- ventilatory response and the arterial level of carbon dioxide. toire et les niveaux de C02 artdriels. Le chimior~flexe ptariph~- The peripheral chemoreflex, the ventilatory response to carbon rique, la r~ponse ventilatoire au C02 et I'hypoxie mddi~s par les dioxide and hypoxia mediated by the peripheral chemorecep- chEmorEcepteurs p~riph~riques sont subdivis~es en deux rela- tors, is broken into two relations. First, a straight.line relation tions. PremiErement, une relation directe entre la rdponse between the ventilatory response and the arterial level of carbon ventilatoire et le niveau artEriel de COz dont la pente (sensiti- dioxide whose slope (sensitivity) increases as the oxygen level vitE) augmente a vec les variations du niveau d' oxygEne d' hyper- varies from hyperoxic to hypoxic. Second, a rectangular oxique c} hypoxique. Deuxidmement, une relation hyperbolique hyperbolic relation between the ventilatory response and the rectangulaire entre la rdponse respiratoire et le niveau artEriel arterial level of oxygen with ventilation increasing with increas- d' oxygOne avecla ventilation augmentant avec I' augmentation ing hypoxia. The three ventilatory response relations (one de l'hypoxie.
    [Show full text]
  • Regulation of Ventilation
    CHAPTER 1 Regulation of Ventilation © IT Stock/Polka Dot/ inkstock Chapter Objectives By studying this chapter, you should be able to do 5. Describe the chemoreceptor input to the brain the following: stem and how it modifi es the rate and depth of breathing. 1. Describe the brain stem structures that regulate 6. Explain why it is that the arterial gases and pH respiration. do not signifi cantly change during moderate 2. Defi ne central and peripheral chemoreceptors. exercise. 3. Explain what eff ect a decrease in blood pH or 7. Discuss the respiratory muscles at rest and carbon dioxide has on respiratory rate. during exercise. How are they infl uenced by 4. Describe the Hering–Breuer reflex and its endurance training? function. 8. Describe respiratory adaptations that occur in response to athletic training. Chapter Outline Passive and Active Expiration Eff ects of Blood PCO 2 and pH on Ventilation Respiratory Areas in the Brain Stem Proprioceptive Refl exes Dorsal Respiratory Group Other Factors Ventral Respiratory Group Hering–Breuer Refl ex Apneustic Center Ventilation Response During Exercise Pneumotaxic Center Ventilation Equivalent for Oxygen () V/EOV 2 Chemoreceptors Ventilation Equivalent for Carbon Dioxide Central Chemoreceptors ()V/ECV O2 Peripheral Chemoreceptors Ventilation Limitations to Exercise Eff ects of Blood PO 2 on Ventilation Energy Cost of Breathing Ventilation Control During Exercise Chemical Factors Copyright ©2014 Jones & Bartlett Learning, LLC, an Ascend Learning Company Content not final. Not for sale or distribution. 17097_CH01_Pass4.indd 3 10/12/12 2:13 PM 4 Chapter 1 Regulation of Ventilation Passive and Active Expiration Ventilation is controlled by a complex cyclic neural process within the respiratory Brain stem Th e lower part centers located in the medulla oblongata of the brain stem .
    [Show full text]
  • Pulmonary Ventilation
    CHAPTER 2 Pulmonary Ventilation © IT Stock/Polka Dot/ inkstock Chapter Objectives By studying this chapter, you should be able to do Name two things that cause pleural pressure the following: to decrease. 8. Describe the mechanics of ventilation with 1. Identify the basic structures of the conducting respect to the changes in pulmonary pressures. and respiratory zones of the ventilation system. 9. Identify the muscles involved in inspiration and 2. Explain the role of minute ventilation and its expiration at rest. relationship to the function of the heart in the 10. Describe the partial pressures of oxygen and production of energy at the tissues. carbon dioxide in the alveoli, lung capillaries, 3. Identify the diff erent ways in which carbon tissue capillaries, and tissues. dioxide is transported from the tissues to the 11. Describe how carbon dioxide is transported in lungs. the blood. 4. Explain the respiratory advantage of breathing 12. Explain the significance of the oxygen– depth versus rate during a treadmill exercise. hemoglobin dissociation curve. 5. Describe the composition of ambient air and 13. Discuss the eff ects of decreasing pH, increasing alveolar air and the pressure changes in the pleu- temperature, and increasing 2,3-diphosphoglyc- ral and pulmonary spaces. erate on the HbO dissociation curve. 6. Diagram the three ways in which carbon dioxide 2 14. Distinguish between and explain external res- is transported in the venous blood to the lungs. piration and internal respiration. 7. Defi ne pleural pressure. What happens to alve- olar volume when pleural pressure decreases? Chapter Outline Pulmonary Structure and Function Pulmonary Volumes and Capacities Anatomy of Ventilation Lung Volumes and Capacities Lungs Pulmonary Ventilation Mechanics of Ventilation Minute Ventilation Inspiration Alveolar Ventilation Expiration Pressure Changes Copyright ©2014 Jones & Bartlett Learning, LLC, an Ascend Learning Company Content not final.
    [Show full text]
  • Reviews the Control of Breathing in Clinical Practice*
    Reviews The Control of Breathing in Clinical Practice* Brendan Caruana-Montaldo, MD; Kevin Gleeson, MD; and Clifford W. Zwillich, MD, FCCP The control of breathing results from a complex interaction involving the respiratory centers, which feed signals to a central control mechanism that, in turn, provides output to the effector muscles. In this review, we describe the individual elements of this system, and what is known about their function in man. We outline clinically relevant aspects of the integration of human ventilatory control system, and describe altered function in response to special circumstances, disorders, and medications. We emphasize the clinical relevance of this topic by employing case presentations of active patients from our practice. (CHEST 2000; 117:205–225) Key words: carotid body; chemoreceptors; control of ventilation; pulmonary receptors Abbreviations: CPAP 5 continuous positive airway pressure; CSF 5 cerebrospinal fluid; CSR 5 Cheyne-Stokes 5 1 5 2 5 respiration; DRG dorsal respiratory group; [H ] hydrogen ion concentration; HCO3 bicarbonate; MVV 5 maximal voluntary ventilation; OSA 5 obstructive sleep apnea; pHa 5 arterial pH; PIIA 5 postinspiration inspiratory activity; PImax 5 maximal inspiratory pressure; RAR 5 rapidly adapting receptor; REM 5 rapid eye 5 5 5 ˙ 5 movement; Sao2 arterial oxygen saturation; SAR slowly adapting receptor; VC vital capacity; Ve minute ˙ 5 ˙ ˙ 5 5 5 ventilation; Vo2 oxygen uptake; V/Q ventilation/perfusion; VRG ventral respiratory group; Vt tidal volume; WOB 5 work of breathing his review is intended as an overview of human response to changes in blood chemistry, mechanical T respiratory control. The first section will briefly load, metabolic rate, and respiratory neural receptors describe the physiology of respiratory control includ- enables the respiratory system to adapt to special ing the sensors, the central controllers, and the physiologic circumstances such as sleep, exercise, effector systems.
    [Show full text]
  • Respiration Lesson 7
    Respiration Lesson 7 Objectives • Identify where in the brain the basic rhythm of breathing is generated. • Specify the key sources of sensory information to the medullary respiratory center that modify its output to the respiratory muscles. • Provide examples of modification arising from pontine structures lung mechanoreceptors. central & peripheral chemoreceptors • Describe the sequence of events by which changes in arterial levels PCO2, PO2 & pH stimulate ventilation. 5) Explain why increases in arterial hydrogen ion concentration do not stimulate the central chemoreceptors. Respiration Lesson 7 • What is it that the respiratory control system controls? • What is the primary drive to breathe in man at rest? • What is the primary stimulus to increase ventilation during exercise? 1 Control of Breathing Components of the neural control system What is controlled? respiratory center : medulla chemoreceptor spinal cord respiratory muscles movement of chest wall & lungs ventilation alveolar-capillary membrane gas exchange arterial blood PCO2 , PO2 , pH Control of Breathing Respiratory Centres in the brainstem establish a rhythmic breathing pattern Whereas the heart can generate its own rhythm due to intrinsic pacemaker activity, the respiratory muscles are skeletal and are innervated by spinal nerves which require neural stimulation. The rhythmic neural activity that establishes the normal breathing pattern arises in the PreBötzinger medulla complex 2 Control of Breathing Breathing Is Initiated in the Medulla The Medullary Respiratory Centres consist of the: PreBötzinger Complex Most researchers currently believe that this is the source of the respiratory rhythm PreBötzinger complex Control of Breathing Breathing Is Initiated in the Medulla The Medullary Respiratory Centres consist of the: Dorsal Respiratory Group These cells reside in the nucleus tractus solitarius.
    [Show full text]
  • Basing Respiratory Management of Coronavirus on Physiological Principles
    Page 1 of 9 Basing Respiratory Management of Coronavirus on Physiological Principles Martin J. Tobin MD, Division of Pulmonary and Critical Care Medicine, Hines Veterans Affairs Hospital and Loyola University of Chicago Stritch School of Medicine, Hines, Illinois 60141 (E-mail address: [email protected]; Telephone: 708-202-2705) Page 2 of 9 The dominant respiratory feature of severe coronavirus disease 2019 (Covid-19) is arterial hypoxemia, greatly exceeding abnormalities in pulmonary mechanics (decreased compliance).1-3 Many patients are intubated and placed on mechanical ventilation early in their course. Projections on usage of ventilators has led to fears that insufficient machines will be available, and even to proposals for employing a single machine to ventilate four patients. The coronavirus crisis poses challenges for staffing, equipment and resources, but it also imposes cognitive challenges for physicians at the bedside. It is vital that caregivers base clinical decisions on sound scientific knowledge in order to gain the greatest value from available resources.4 Patient oxygenation is evaluated initially using a pulse oximeter. Oximetry estimated saturation (SpO2) can differ from true arterial oxygen saturation (SaO2, measured with a co-oximeter) by as much as + 4%.5 Interpretation of SpO2 readings above 90% becomes especially challenging because of the sigmoid shape of the oxygen-dissociation curve. Given the flatness of the upper oxygen-dissociation curve, a pulse oximetry reading of 95% can signify an arterial oxygen tension (PaO2) anywhere between 60 and 200 mmHg6,7—values that carry extremely different connotations for management of a patient receiving a high concentration of oxygen. Difficulties in interpreting arterial oxygenation are compounded if supplemental oxygen has been instituted before a pulmonologist or intensivist first sees a patient (usual scenario with Covid-19).
    [Show full text]
  • Pulmonary Blood Flow Distribution and Hypoxic Pulmonary Vasoconstriction in Pentobarbital-Anesthetized Horses
    PULMONARY BLOOD FLOW DISTRIBUTION AND HYPOXIC PULMONARY VASOCONSTRICTION IN PENTOBARBITAL-ANESTHETIZED HORSES DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Phillip Lerche, BVSc MS ***** The Ohio State University 2006 Dissertation Committee: Approved by Dr William W Muir III, Adviser Dr Robert L Hamlin ________________________ Dr John AE Hubbell Adviser Graduate Program in Veterinary Clinical Sciences ABSTRACT Anesthetized horses commonly develop undesirable hypoxemia when dorsally recumbent. The major reason for this is development of ventilation/perfusion (V/Q) mismatching associated with atelectasis of dependent lung tissue. Improving ventilation frequently does not improve oxygenation, suggesting that pulmonary blood flow distribution is abnormal during anesthesia. Perfusion is normally matched to ventilation by hypoxic pulmonary vasoconstriction (HPV). This mechanism causes pulmonary arterioles to constrict in areas where alveolar oxygen (O 2) tension is low, redirecting blood flow to better-ventilated alveoli, and is believed to be modulated by nitric oxide (NO). The purpose of this study was to evaluate blood flow distribution in the anesthetized horse and to investigate the role of NO as a regulator of HPV in the anesthetized dorsally recumbent adult horse. Six adult horses anesthetized with pentobarbital were intubated via tracheostomy with a double-lumen tube, which separated gas flow to left and right lungs. Each lung was individually ventilated via a dual-lung ventilator, and 100% O 2 was delivered to both lungs. A hypoxic/hyperoxic state was then induced by ventilating the left lung with 100% nitrogen (N 2) while 100% O 2 was delivered to the right lung.
    [Show full text]
  • Physiology of the Respiratory Drive in ICU Patients: Implications for Diagnosis and Treatment Annemijn H
    Jonkman et al. Critical Care (2020) 24:104 https://doi.org/10.1186/s13054-020-2776-z REVIEW Open Access Physiology of the Respiratory Drive in ICU Patients: Implications for Diagnosis and Treatment Annemijn H. Jonkman1,2†, Heder J. de Vries1,2† and Leo M. A. Heunks1,2* Abstract This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2020. Other selected articles can be found online at https://www.biomedcentral.com/collections/annualupdate2020. Further information about the Annual Update in Intensive Care and Emergency Medicine is available from http:// www.springer.com/series/8901. Introduction chapter is to discuss the (patho)physiology of respiratory The primary goal of the respiratory system is gas ex- drive, as relevant to critically ill ventilated patients. We change, especially the uptake of oxygen and elimination discuss the clinical consequences of high and low re- of carbon dioxide. The latter plays an important role in spiratory drive and evaluate techniques that can be used maintaining acid-base homeostasis. This requires tight to assess respiratory drive at the bedside. Finally, we control of ventilation by the respiratory centers in the propose optimal ranges for respiratory drive and breath- brain stem. The respiratory drive is the intensity of the ing effort, and discuss interventions that can be used to output of the respiratory centers, and determines the modulate a patient’s respiratory drive. mechanical output of the respiratory muscles (also known as breathing effort) [1, 2]. Detrimental respiratory drive is an important contribu- Definition of Respiratory Drive tor to inadequate mechanical output of the respiratory The term “respiratory drive” is frequently used, but is muscles, and may therefore contribute to the onset, dur- rarely precisely defined.
    [Show full text]
  • Control of Ventilation
    Control of ventilation Under construction Do not edit, change or move this article, please. If you have some comments or suggestions, use the discussion page (https://w ww.wikilectures.eu/index.php?title=Talk:Control_of_ventilation&action=edit). You can also contact the author of this page - you will find their name in history (https://www.wikilectures.eu/index.php?title=Control_of_ventilation&action=history) of this page. Last update: Tuesday, 02 Feb 2021 at 9:54 pm. Control of Ventilation (by Coiled) CNS control of ventilation: The control of breathing by the CNS can be split into three main groups: Those controlled by the group of structures located in the Medulla (the Dorsal Respiratory Group and the Ventral Respiratory Group), and structures located in the Pons (Pneumotaxic Centre, and Apneustic Centre), and finally those control centers that are located above the brainstem. REMEMBER, the most important two clusters of controllers are in the PONS and MEDULLA 1) Structures located in medulla: Dorsal Respiratory Group (DRG) and Ventral Respiratory Group (VRG) DRG: DRG is the crucial structure for spontaneous inspiration. Located at the dorsal part of the medulla. Uses a “ramp signal” to stimulate diaphragm and other respiratory muscles (You can imagine ramp signal as a burst of action potentials. The frequency of action potentials progressively increases with the depth of the breath. After the burst ceases, the expiration fallows.). This is a pretty good mechanism how to control the length and depth of inspiration. The ramp signal is controlled by the respiratory centres located higher in the brain stem. Receives many peripheral sensory inputs - centripetal fibers of n.
    [Show full text]