![]() This illustrates how physiological factors may lead to a change in RR as a result of a change in SpO2. When ventilation and gas exchange occur, the normal range of oxygen saturation of the blood (SpO2) is 94-98% (O’Driscoll et al, 2017) and this can be maintained at rest with a RR of 12-20 breaths per minute.įig 2 shows the oxyhaemoglobin disassociation curve. For effective gas exchange to take place, air breathed into the lungs must travel to the alveolar membrane where the capillary walls are thin and there is an overall large surface area. The partial pressure of O2 in the atmosphere is higher relative to that in the body and the bloodstream contains a higher partial pressure of CO2 than the atmosphere. A gas will move from an area of high concentration to an area of low concentration. The process of ventilation delivers air to the alveoli where gaseous exchange occurs by a simple process of diffusion. Changes in RR occur in response to exercise, emotions and during sleep those changes in RR associated with exercise and anxiety may be greater than 25 beats per minute but will usually return to normal in a resting, calm state. This movement of the chest wall is observed when respiratory rate (RR) is measured. The visceral pleural layer attached to the surface of the lungs follows and the lungs expand, drawing air in.Įxpiration at rest is a largely passive process inspiratory muscles relax and there is elastic recoil of the lungs giving rise to a state of pressure equilibrium before the cycle begins again (Bourke and Burns, 2015). These changes cause the parietal pleural layer of the lungs to move with the ribcage and diaphragm, creating a negative pressure. ![]() This increases the size of the thoracic cavity. During normal breathing, inspiration occurs by the contraction and flattening of the diaphragm and the contraction of the external intercostal muscles, causing a rise and outward movement of the ribcage. VentilationĪir naturally moves from an area of high pressure to an area of low pressure. This allows for the total surface area of the lung to increase exponentially allowing maximum opportunity for gas exchange.Ĭentral and peripheral chemo receptors sensitive to hypoxia (low O2 levels) and hypercapnia (increased CO2) control the drive to breathe (Davies and Moore, 2010). Alveoli are the site of gas exchange and their presence increases as the airways become smaller. The smaller airways (respiratory bronchioles) contain alveoli in their walls. The airways in each generation arise from the previous one by a system of irregular dichotomous branches (Davies and Moore, 2010). The lungs are made up of large and small airways – the trachea being the largest and first of 23 generations of airways. To understand the process of breathing it is important to be familiar with the anatomy of the thorax and the physiology of the respiratory system. This article is funded by an unrestricted educational grant from Hillrom.Click here to see other articles in this series.Scroll down to read the article or download a print-friendly PDF here (if the PDF fails to fully download please try again using a different browser).This article is open access and can be freely distributed.This article has been double-blind peer reviewed. ![]() Nursing Times 104 6, 43-44.Īuthor: Jessica Hartley is deputy head of lung function at Newcastle upon Tyne Hospitals. The second in our five-part series on respiratory rate describes the process of breathing and how it is affected by ill health.Ĭitation: Hartley J (2018) Respiratory rate 2: anatomy and physiology of breathing. Nurses need to understand the anatomy and physiology of normal breathing to measure respiratory rate and interpret findings. Measurement of respiratory rate is a vital sign.
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