Gas Exchange in the Lungs
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal in Principles of Physiology for the Anaesthetist, 2020
The minute pulmonary ventilation of 5 L/min is the product of tidal volume (500 mL) and respiratory rate, normally 10 breaths per minute. Because of the effects of dead space, the alveoli are ventilated by only 4 L of fresh gas each minute during inspiration, containing 840 mL of oxygen and little or no carbon dioxide. Part of each tidal volume, the dead space, does not reach regions of the lung involved in gas exchange and is therefore exhaled unchanged. Within one expiratory tidal volume, there will be anatomical dead space gas and alveolar dead space gas mixed with gas from alveoli that are both ventilated and perfused and actually take part in gas exchange. Alveolar ventilation delivers oxygen to, and removes carbon dioxide from, the alveolar gas. Tissue metabolism (via pulmonary blood flow) delivers carbon dioxide to, and removes oxygen from, alveolar gas.
Orientation to the cardiopulmonary exercise test
Robert B. Schoene, H. Thomas Robertson in Making Sense of Exercise Testing, 2018
A standard clinical cardiopulmonary exercise test acquires continuous measurements of metabolic, cardiovascular, and respiratory parameters over the course of an 8–15 minute effort in which exercise progresses incrementally from minimal movement to a maximal symptom-limited effort. This chapter describes the equipment needed for these exercise measurements and discusses the progressive work protocol that is used for all of these clinical studies. Throughout a progressive work test, there is a consistent linear relationship between the oxygen consumption of the exercising subject and the power output achieved. Breath-by-breath plots of oxygen uptake and carbon dioxide output during a progressive work test show substantial variability, but this variability is primarily attributable to the variability of breath size and does not represent measurement error or variability in muscle metabolism. The software in integrated exercise systems uses the exercise measurements of gas flow and gas concentrations to calculate breath-by-breath measurements of tidal volume, oxygen uptake, and carbon dioxide output.
Assessment for Rehabilitation of COVID-19
Wenguang Xia, Xiaolin Huang in Rehabilitation from COVID-19, 2021
Rehabilitation training for COVID-19 patients requires professional rehabilitation physicians to formulate exercise prescriptions based on patients’ specific conditions. The formulation of exercise prescription depends on systematic assessment for rehabilitation, which should run through the whole process of rehabilitation treatment. The system of rehabilitation assessment for COVID-19 patients mainly includes assessments for respiratory function, physical function, and psychosocial function. The examination results can determine the degree and type of lung damage caused by the disease, helping clinicians make accurate diagnoses and develop scientific treatment plans. Lung volume includes tidal volume, inspiratory reverse volume, inspiratory capacity, vital capacity, residual volume, functional residual capacity, and total lung capacity, among which vital capacity is the most commonly used. Vital capacity of healthy adults varies greatly depending on genders, ages, body types, and exercises. Common clinical indexes are maximum ventilatory volume, forced vital capacity, or forced expiratory volume.
The volume dependence of stress relaxation in the rat respiratory system
Published in Experimental Lung Research, 2014
Alessandro Rubini, Emanuele Luigi Carniel
ABSTRACT Aim: To investigate the volume dependence of respiratory system stress relaxation in anesthetized, positive-pressure ventilated rats. Materials and methods: The effects on respiratory system stress relaxation of changing the end inflation volume while keeping tidal volume constant, and of changing the tidal volume while maintaining constant end inflation volume, were separately studied by the end-inflation occlusion method. These changes were obtained by inflating the respiratory system starting from different volumes above functional residual capacity. Results: We found that: (1) a simple exponential equation well describe the visco-elastic pressure drop for different inflation modalities; (2) the stress relaxation-linked, visco-elastic pressure drop, increases with increasing the tidal volume and keeping the end-inflation volume constant, but is independent from the end-inflation lung volume at constant tidal volumes; (3) time constant values show a significant increment with end-inflation volume at constant tidal volume but result independent from tidal volume variation at constant end-inflation volume. Conclusions: Stress relaxation-linked pressure dissipation increases with increasing tidal volume independently from end-inspiratory volume.
Effect of low tidal volume during general anesthesia for urological procedures on lung functions
Published in Egyptian Journal of Anaesthesia, 2015
BackgroundPostoperative lung function impairment is common after surgery specially in the lateral decubitus position. Evidence suggests that if we use low tidal volume during mechanical ventilation this may limit post-operative lung injury. We compared post-operative lung functions in patients put in the lateral position when ventilated with low vs. high tidal volumes. MethodsThis prospective open label clinical trial was performed on 104 patients ASA I&II scheduled for elective urological operations done in the right or left lateral position expected to last more than 2 hours. Patients were divided into two groups: group L ventilated with 5–7 ml/kg tidal volume, with positive end expiratory pressure (PEEP) 10 cm H2O and recruitment maneuver (RM) and group H ventilated with 10–12 ml/kg tidal volume with zero-end expiratory pressure and no recruitment maneuver. Pulmonary functions were measured pre-operatively and 6, 12, 24 hours after extubation. ResultsBetter pulmonary functions were found in the first post-operative six hours in the low tidal volume group and significant difference was found in all parameters. FVC and FEV1/FVC were significantly higher in the low tidal volume group (P = 0.000) after 12 hours of extubation. After 24 hours we found significant difference in the predicted FEV1 and FVC and FEV1/FVC ratio (P = 0.000) being higher in the low tidal volume group. ConclusionIn comparison with conventional mechanical ventilation using high tidal volume with zero PEEP and no RM: a lung protective strategy using low tidal volume with 5–10 cm H2O PEEP and RM did improved lung functions in the first post-operative 24 hours. The overall postoperative follow up did not show significant difference between the two groups.
Respiration in Sprague-Dawley Rats During Pregnancy
Published in Inhalation Toxicology, 2006
Teresa L. Leavens, Carl U. Parkinson, R. Arden James, Dennis House, Barbara Elswick, David C. Dorman
Minute ventilation and tidal volume increase in humans during pregnancy. Little data exists, however, on the respiration in pregnant rats, despite their widespread use as an animal model. Since respiration will affect the pharmacokinetics of volatile compounds and ultimately the dose to the fetus, we conducted a study to evaluate respiration in rats during pregnancy. Whole-body plethysmography was used to measure the breathing frequency and tidal volume approximately every other day from gestation day (GD) 1 to 21 in 16 timed pregnant and 16 nonpregnant, female, Sprague-Dawley rats. Minute ventilation was calculated as a product of the breathing frequency and tidal volume, and the body weight of each rat was used to determine the scaled ventilation. Multivariate analysis of variance methods for a repeated-measures design were used to analyze the respiratory data. Breathing frequency was not affected by pregnancy; however, tidal volume was somewhat greater in pregnant versus nonpregnant rats. The increase in tidal volume resulted in significantly increased minute ventilation in pregnant rats compared to nonpregnant rats during the latter period of gestation. Due to the increased body weight of the pregnant rats, the scaled ventilation at the end of gestation was significantly lower in pregnant rats compared to nonpregnant rats. This study provides important reference values that can be used in pharmacokinetic models during pregnancy.
Related Knowledge Centers
- Acute Respiratory Distress Syndrome
- Lung Volumes
- Nebulizer
- Mechanical Ventilation
- Positive End-Expiratory Pressure