Researchers discovered that the sternocleidomastoid muscle may be used excessively as an accessory respiratory muscle in patients with pulmonary arterial hypertension (PAH), according to a study published in Heart & Lung. 

PAH can often lead to vasculopathy of the distal pulmonary arterial circulation, predisposing an individual to heart failure and death. Exertional dyspnea and exercise intolerance are characteristic symptoms of the disease. 

A common complication of PAH is morphological and functional impairment of the skeletal and respiratory muscles, given that the circulatory system is compromised. Impairment of muscle strength, in turn, can give rise to additional negative health effects such as further limitations to an individual’s exercise capacity. 

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The authors of the study thus set out to investigate if the primary and accessory respiratory muscles differ in strength compared with healthy controls. The research team recruited patients with PAH (n=27) admitted to the department of cardiology at Istanbul University between September and December 2021. Age- and sex-matched controls from the community were also recruited. 

Read more about PAH etiology 

Respiratory muscle strength was assessed via maximal inspiratory and expiratory pressures through a mouth pressure device. Accessory respiratory muscle strength was assessed by asking participants to complete various muscle movements, some with resistance. In addition, participants were also asked to complete the 6-minute walk test as a measure of their exercise capacity. 

The results of the study revealed that the strength of the respiratory muscles was reduced except for the sternocleidomastoid muscle. In addition, exercise capacity was lower in the cohort of patients with PAH compared with the control. The researchers also reported that respiratory and quadriceps muscle strength correlated with patient exercise capacity. 

The authors theorized that the sternocleidomastoid muscle may be excessively used to compensate for the diminished role of the diaphragmatic muscles during inspiration in patients with PAH. 

“It should also be investigated whether strengthening the accessory muscles via rehabilitative approaches such as upper extremity training will improve exercise capacity,” the authors wrote. 


Durdu H, Demir R, Zeren M, et al. Evaluation of primary and accessory respiratory muscles and their influence on exercise capacity and dyspnea in pulmonary arterial hypertensionHeart Lung. 2022;57:173-179. doi:10.1016/j.hrtlng.2022.09.015