Transpulmonary pressure

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Transpulmonary pressure is the difference between the alveolar pressure and the intrapleural pressure in the pleural cavity. During human ventilation, air flows because of pressure gradients.

Contents

Ptp = Palv – Pip

Where Ptp is transpulmonary pressure, Palv is alveolar pressure, and Pip is intrapleural pressure.

Physiology

Since atmospheric pressure is relatively constant, pressure in the lungs must be higher or lower than atmospheric pressure for air to flow between the atmosphere and the alveoli. If 'transpulmonary pressure' = 0 (alveolar pressure = intrapleural pressure), such as when the lungs are removed from the chest cavity or air enters the intrapleural space (a pneumothorax), the lungs collapse as a result of their inherent elastic recoil. Under physiological conditions the transpulmonary pressure is always positive; intrapleural pressure is always negative and relatively large, while alveolar pressure moves from slightly negative to slightly positive as a person breathes. For a given lung volume, the transpulmonary pressure is equal and opposite to the elastic recoil pressure of the lung.

The transpulmonary pressure vs volume curve of inhalation (usually plotted as volume as a function of pressure) is different from that of exhalation, the difference being described as hysteresis. Lung volume at any given pressure during inhalation is less than the lung volume at any given pressure during exhalation. [1]

Measurement

Transpulmonary pressure can be measured by placing pressure transducers. The alveolar pressure is estimated by measuring the pressure in the airways while holding one's breath. [2] The intrapleural pressure is estimated by measuring the pressure inside a balloon placed in the esophagus. [2]

Measurement of transpulmonary pressure assists in spirometry in availing for calculation of static lung compliance.

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The respiratory system is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies greatly, depending on the size of the organism, the environment in which it lives and its evolutionary history. In land animals, the respiratory surface is internalized as linings of the lungs. Gas exchange in the lungs occurs in millions of small air sacs; in mammals and reptiles, these are called alveoli, and in birds, they are known as atria. These microscopic air sacs have a very rich blood supply, thus bringing the air into close contact with the blood. These air sacs communicate with the external environment via a system of airways, or hollow tubes, of which the largest is the trachea, which branches in the middle of the chest into the two main bronchi. These enter the lungs where they branch into progressively narrower secondary and tertiary bronchi that branch into numerous smaller tubes, the bronchioles. In birds, the bronchioles are termed parabronchi. It is the bronchioles, or parabronchi that generally open into the microscopic alveoli in mammals and atria in birds. Air has to be pumped from the environment into the alveoli or atria by the process of breathing which involves the muscles of respiration.

Dead space is the volume of air that is inhaled that does not take part in the gas exchange, because it either remains in the conducting airways or reaches alveoli that are not perfused or poorly perfused. It means that not all the air in each breath is available for the exchange of oxygen and carbon dioxide. Mammals breathe in and out of their lungs, wasting that part of the inhalation which remains in the conducting airways where no gas exchange can occur.

<span class="mw-page-title-main">Mechanical ventilation</span> Method to mechanically assist or replace spontaneous breathing

Mechanical ventilation or assisted ventilation is the medical term for using a machine called a ventilator to fully or partially provide artificial ventilation. Mechanical ventilation helps move air into and out of the lungs, with the main goal of helping the delivery of oxygen and removal of carbon dioxide. Mechanical ventilation is used for many reasons, including to protect the airway due to mechanical or neurologic cause, to ensure adequate oxygenation, or to remove excess carbon dioxide from the lungs. Various healthcare providers are involved with the use of mechanical ventilation and people who require ventilators are typically monitored in an intensive care unit.

<span class="mw-page-title-main">Respiratory tract</span> Organs involved in transmission of air to and from the point where gases diffuse into tissue

The respiratory tract is the subdivision of the respiratory system involved with the process of conducting air to the alveoli for the purposes of gas exchange in mammals. The respiratory tract is lined with respiratory epithelium as respiratory mucosa.

<span class="mw-page-title-main">Gas exchange</span> Process by which gases diffuse through a biological membrane

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<span class="mw-page-title-main">Inhalation</span> Flow of the respiratory current into an organism

Inhalation is the process of drawing air or other gases into the respiratory tract, primarily for the purpose of bringing oxygen into the body. It is a fundamental physiological function in humans and many other organisms, essential for sustaining life. Inhalation is the first phase of breathing, allowing the exchange of oxygen and carbon dioxide between the body and the environment, vital for the body's metabolic processes. This article delves into the mechanics of inhalation, its significance in various contexts, and its potential impact on health.

<span class="mw-page-title-main">Exhalation</span> Flow of the respiratory current out of an organism

Exhalation is the flow of the breath out of an organism. In animals, it is the movement of air from the lungs out of the airways, to the external environment during breathing. This happens due to elastic properties of the lungs, as well as the internal intercostal muscles which lower the rib cage and decrease thoracic volume. As the thoracic diaphragm relaxes during exhalation it causes the tissue it has depressed to rise superiorly and put pressure on the lungs to expel the air. During forced exhalation, as when blowing out a candle, expiratory muscles including the abdominal muscles and internal intercostal muscles generate abdominal and thoracic pressure, which forces air out of the lungs.

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Lung compliance, or pulmonary compliance, is a measure of the lung's ability to stretch and expand. In clinical practice it is separated into two different measurements, static compliance and dynamic compliance. Static lung compliance is the change in volume for any given applied pressure. Dynamic lung compliance is the compliance of the lung at any given time during actual movement of air.

<span class="mw-page-title-main">Muscles of respiration</span> Muscles involved in breathing

The muscles of respiration are the muscles that contribute to inhalation and exhalation, by aiding in the expansion and contraction of the thoracic cavity. The diaphragm and, to a lesser extent, the intercostal muscles drive respiration during quiet breathing. The elasticity of these muscles is crucial to the health of the respiratory system and to maximize its functional capabilities.

<span class="mw-page-title-main">Breathing</span> Process of moving air in and out of the lungs

Breathing is the rhythmical process of moving air into (inhalation) and out of (exhalation) the lungs to facilitate gas exchange with the internal environment, mostly to flush out carbon dioxide and bring in oxygen.

ΔP is a mathematical term symbolizing a change (Δ) in pressure (P).

<span class="mw-page-title-main">Alveolar pressure</span> Air pressure inside lung alveoli

Alveolar pressure (Palv) is the pressure of air inside the lung alveoli. When the glottis is opened and no air is flowing into or out of the lungs, alveolar pressure is equal to the atmospheric pressure, that is, zero cmH2O.

<span class="mw-page-title-main">Intrapleural pressure</span> Refers to the pressure within the pleural cavity

In physiology, intrapleural pressure refers to the pressure within the pleural cavity. Normally, the pressure within the pleural cavity is slightly less than the atmospheric pressure, which is known as negative pressure. When the pleural cavity is damaged or ruptured and the intrapleural pressure becomes greater than the atmospheric pressure, pneumothorax may ensue.

A negative pressure ventilator (NPV) is a type of mechanical ventilator that stimulates an ill person's breathing by periodically applying negative air pressure to their body to expand and contract the chest cavity.

<span class="mw-page-title-main">Pulmonary pleurae</span> Membrane lining the thoracic cavity wall

The pulmonary pleurae are the two flattened sacs ensheathing each lung, locally appearing as two opposing layers of serous membrane separating the lungs from the mediastinum and the inside surfaces of the surrounding chest walls.

Work of breathing (WOB) is the energy expended to inhale and exhale a breathing gas. It is usually expressed as work per unit volume, for example, joules/litre, or as a work rate (power), such as joules/min or equivalent units, as it is not particularly useful without a reference to volume or time. It can be calculated in terms of the pulmonary pressure multiplied by the change in pulmonary volume, or in terms of the oxygen consumption attributable to breathing.

Dynamic compression of the airways results when intrapleural pressure equals or exceeds alveolar pressure, which causes dynamic collapsing of the lung airways. It is termed dynamic given the transpulmonary pressure varies based on factors including lung volume, compliance, resistance, existing pathologies, etc.

<span class="mw-page-title-main">Ventilation–perfusion coupling</span> Relationship between respiratory and cardiovascular processes

Ventilation-perfusion coupling is the relationship between ventilation and perfusion processes, which take place in the respiratory system and the cardiovascular system. Ventilation is the movement of gas during breathing, and perfusion is the process of pulmonary blood circulation, which delivers oxygen to body tissues. Anatomically, the lung structure, alveolar organization, and alveolar capillaries contribute to the physiological mechanism of ventilation and perfusion. Ventilation-perfusion coupling maintains a constant ventilation/perfusion ratio near 0.8 on average, while the regional variation exists within the lungs due to gravity. When the ratio gets above or below 0.8, it is considered abnormal ventilation-perfusion coupling, also known as a ventilation–perfusion mismatch. Lung diseases, cardiac shunts, and smoking can cause a ventilation-perfusion mismatch that results in significant symptoms and diseases, which can be treated through treatments like bronchodilators and oxygen therapy.

References

  1. John B. West (2005). Respiratory physiology: the essentials. Hagerstown, MD: Lippincott Williams & Wilkins. ISBN   0-7817-5152-7.
  2. 1 2 Ronald B. George (2005) Chest medicine: essentials of pulmonary and critical care medicine. ISBN   978-0-7817-5273-2. p. 96 .