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Clinical Workflows Supported by Patient Care Device Data
Published in John R. Zaleski, Clinical Surveillance, 2020
A patient’s ability to sustain spontaneous breathing is determined by the level of carbon dioxide in the bloodstream, and the patient’s stamina based on the ability to support the volume and pressure loads placed on the patient’s respiratory muscles. These volume and pressure loads are assessed using specific tests (i.e., the negative inspiratory force and vital capacity tests). The volume loads are evaluated by measuring the minute ventilation requirements of the patient, typically in terms of “dead space” volume versus tidal volume, or VD/VT. The term “dead space” refers to air that is inhaled during breathing but that does not take place in the gas exchange process. The relationship between dead space ventilation and tidal volume is given by Equation 5.9 [110]:VDVT=PaCO2−PeCO2PaCO2
Basic Concepts of Exposure and Response
Published in Stephen K. Hall, Joana Chakraborty, Randall J. Ruch, Chemical Exposure and Toxic Responses, 2020
There are several air volumes which are used to describe the process of respiration. The “dead space” is the volume of the respiratory tree apart from the alveolar region where oxygen and carbon dioxide are exchanged. The last 150 cc of air inspired and the first 150 cc exhaled are composed of “dead space” air. Emphysema results in a great increase in this volume and a decrease in the efficiency of respiration. The “vital capacity” is the volume of air involved in respiration when inspiration and expiration are performed with maximal effort. The “residual volume” is the volume of air remaining in the lung after a maximal expiratory effort. Gaseous agents are slowly released from the alveolar space on expiration due to the slow release of this volume. Therefore, several expirations are required to rid the lung of residual toxicant once an individual begins breathing clean air.
Physiology of the Airways
Published in Anthony J. Hickey, Sandro R.P. da Rocha, Pharmaceutical Inhalation Aerosol Technology, 2019
Anthony J. Hickey, David C. Thompson
The dead space (the volume of airway not involved indirectly in gas exchange) confers a buffering capacity on the airways in that, for each breath, air taken in from the external environment or alveolar air must mix with dead space air. This process, although decreasing the efficiency with which oxygen is delivered to and carbon dioxide is removed from the alveolar space (e.g. dead space oxygen concentration will be determined by the oxygen concentration of air inhaled from the external environment and of that in the alveolar space that was shunted into the dead space in the previous breath), serves to even out the alveolar gas concentrations by preventing dramatic swings in alveolar gas concentrations that would occur if the alveolar air were exchanged completely during each breath. It should be recognized that the volume of the dead space is not insignificant. For example, in a normal tidal breath of 500 mL–600 mL, 150 mL represents dead space volume.
Cardiopulmonary parameters and organ blood flows for workers expressed in terms of VO2 for use in physiologically based toxicokinetic modeling
Published in Journal of Toxicology and Environmental Health, Part A, 2022
Pierre Brochu, Jessie Ménard, Sami Haddad
It is well-known that physiological dead space (VDphys in L) includes volumes of the conducting airway referred to as anatomical dead space (Folkow and Pappenheimer 1955; Fowler 1948) and some under-perfused or poorly perfused alveoli not contributing or poorly contributing to the gas exchange (Bohr 1891; Enghoff 1938; Guyton and Hall 2006). The VE (in L/min) corresponds to the inspired tidal volume (VT in L) multiplied by the respiratory rate (f in number of breaths per minute), whereas the VA (in L/min) is defined as the fraction of the inspired tidal volume per minute (thus VE) which participates in gas exchange (Guyton and Hall 2006). This is mathematically summarized as follows (Guyton and Hall 2006):