Mismatch and Shunt
Lara Wijayasiri, Kate McCombe, Paul Hatton, David Bogod in The Primary FRCA Structured Oral Examination Study Guide 1, 2017
How does ventilation vary from the apex to the base of the lung?The lungs are suspended within the thoracic cavity and therefore the alveoli are subjected to the effects of gravity.In the upright lung intrapleural pressure varies from the top to the base of the lungs. For every centimetre of vertical displacement from the tip of the lung to the base, intrapleural pressure increases by about 0.2 cm H2O.For an average healthy male, the intrapleural pressure at the apex of the lung is about −8 cm H2O and at the base is about −1.5 cm H2O. This means that the alveoli at the apex are exposed to a greater distending pressure compared to those at the base.Consequently, the alveoli at the lung apex are relatively larger than those at the bases. The apical alveoli are thus on a flatter part of their pressure–volume (i.e. compliance) curve than the basal alveoli, which are on the steep portion of the compliance curve. Therefore, being relatively more compliant, the alveoli at the base fill to a greater extent for a given change in intrapleural pressure during inspiration compared to the alveoli at the apex. Hence, ventilation is preferentially distributed to the basal alveoli.
Functions of the Respiratory System
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal in Principles of Physiology for the Anaesthetist, 2020
The lungs lie within the thorax, covered by the visceral pleura and separated from the parietal pleura on the inside of the chest wall by the (potential) intrapleural space. The diaphragm separates the lungs from the abdominal contents. The elastic forces of the lung and the chest wall are in equilibrium; the tendency of the lung is to collapse (contract down), and the tendency of the chest wall is to expand (muscle tone in the diaphragm also contributes to this), resulting in a negative intrapleural pressure (Figure 15.1). Therefore, the transmural pressure gradient that tends to distend the alveolar wall (called the transpulmonary pressure) increases. Transpulmonary pressure is the difference between alveolar and intrapleural pressures. At the end of a normal expiration, the two opposing forces balance and the lung volume is at FRC.
Diseases of the pleura
Louis-Philippe Boulet in Applied Respiratory Pathophysiology, 2017
Each gas contained in the pleural space is reabsorbed independently of the others, resorption taking place gradually and in successive phases. During the first phase, there is equilibration of oxygen and carbon dioxide partial pressures and during the second phase, there is progressive resorption of the remaining intrapleural gases like nitrogen. Gradually, the intrapleural pressure recovers its normal negative pressure thus favoring lung reexpansion. The composition of gases in the pleural space can also vary and influence its rate of resorption. For example, oxygen is more diffusible and soluble than other gases, and thus its transfer from pleura to circulation is faster than that of carbon dioxide or nitrogen.
Endobronchial valve therapy for severe emphysema: an overview of valve-related complications and its management
Published in Expert Review of Respiratory Medicine, 2020
T. David Koster, Karin Klooster, Nick H. T. Ten Hacken, Marlies van Dijk, Dirk-Jan Slebos
Another potential manifestation is the ‘pneumothorax ex vacuo’, which means there is air in the pleural space, but no active air leak. There are two hypotheses as to how this develops. It is possible that there is a trauma of the treated lobe in which a part of the volume expands to the pleural cavity, but the valves prevent an active air leak. Most often, the size of the pneumothorax is small [42]. Another hypothesis is that due to the increase in negative intrapleural pressure after the acute lobar collapse, air from the surrounding tissue and blood is drawn into the pleural space. In this case, the pleura remains intact and there is no bronchopleural fistula [42,43]. In case of a pneumothorax ex vacuo, drainage is normally not necessary and a ‘wait-and-see’ policy can be successful in these patients as the pneumothorax will slowly resolve (Figure 8).
Effects of nitrous acid exposure on baseline pulmonary resistance and Muc5ac in rats
Published in Inhalation Toxicology, 2018
Masayuki Ohyama, Ichiro Horie, Yoichiro Isohama, Kenichi Azuma, Shuichi Adachi, Chika Minejima, Norimichi Takenaka
Baseline RLung and baseline Cdyn were measured by tracheal cannulation using a PULMOS-II system (MIPS Co. Ltd., Osaka, Japan) in three consecutive days. Three rats were measured per day in each group in the order of C group, M group, and H group. The rats were anesthetized i.p. with urethane (1 g/kg, 20% w/v). The tip of the tracheal tube was inserted into the trachea through an open tracheostomy. The transpulmonary pressure was determined by monitoring the difference between pressure in the external end of the tracheal cannula and the esophageal cannula using a Statham differential transducer (DP-45; Validyne Engineering corp., Northridge, CA, USA). The intrapleural pressure was measured through a water-filled cannula that was placed in the lower third of the esophagus and connected to one port of a differential pressure transducer (DP-45; Validyne Engineering corp., Northridge, CA, USA). A Fleisch pneumotachograph and a differential transducer were used to monitor the respiratory flow rate (PULMOS-II system; MIPS Co. Ltd., Osaka, Japan). Baseline RLung and baseline Cdyn were estimated under artificial ventilation with a Shinano Respirator (Model SN-480-7; Shinano, Tokyo, Japan) at a respiration rate of 70 breaths/min and a tidal volume of 7 mL/kg (Giles et al., 1971; Filep et al., 2016). The baseline RLung and baseline Cdyn are calculated for each breath. The mean of 20 breaths for the baseline RLung and baseline Cdyn was taken for each rat. The PULMOS-II system was calibrated before and after the measurement, and the calibration error was less than 5%.
Pleural Pressure Differences Before Removal Are Greater in Patients Who Develop Residual Pneumothorax Post Chest Drain Removal
Published in Journal of Investigative Surgery, 2020
Vasileios K. Kouritas, Charalambos Zissis, Ion Bellenis
Traditionally, a “big swing” observed on the fluid column of the underwater drainage system has intrigued clinicians regarding the safety of its removal [6, 11]. In such cases, for increased safety, some clinicians prefer to clamp the drain for a period of time before removal [11]. The association of wide intrapleural pressure differences with prolonged air leak has previously been published [8]. Another reason for a “big swing” is historically perceived to be the presence of a space within the pleural cavity or atelectasis of the lung parenchyma. Results from the present study show that a “big swing”, observed as a wide ΔP, without an obvious space or atelectasis on the chest radiograph before drain removal, was predictive of the presence of residual pneumothorax, especially if it is more than 8 cm H2O. A ΔP more than 12 cm H2O was predictive of the requirement for re-insertion of the chest tube, although no air leak could be identified clinically and no abnormalities were seen on the chest radiograph prior to removal.
Related Knowledge Centers
- Physiology
- Pleural Cavity
- Pneumothorax
- Thoracic Cavity
- Transpulmonary Pressure
- Elastic Recoil
- Müller'S Maneuver
- Pco2
- Glottis
- Diaphragmatic Breathing