Features of inspiratory muscles’ functional state in chronic heart failure with preserved ejection fraction

BACKGROUND: It is known that chronic heart failure contributes to the development of multiple organ pathology, including skeletal muscle pathology.

AIM: To determine the strength and electrical activity of the inspiratory muscles in patients with chronic heart failure with preserved left ventricular ejection fraction.

MATERIAL AND METHODS: The study involved 80 patients of both sexes aged 45 to 74 years, who were divided into three groups: the first group consisted of 24 patients with stage IIA chronic heart failure, the second group consisted of 20 patients with stage I chronic heart failure, and the third group (control group) consisted of 36 patients without chronic heart failure. All patients underwent serum N-terminal fragment of natriuretic brain propeptide determination, 6-minute walk test, measurement of inspiratory muscle strength, and surface electromyography of the inspiratory muscles using three exercise tests. The statistical significance of differences between the groups was assessed using the Mann–Whitney test and Pearson χ².

RESULTS: It was found that when dividing the groups by gender, the maximum inspiratory pressure in women of the first group was lower than in women of the control group by 31.5% (p=0.006). In patients of the first group, a smaller increase in the amplitude of the diaphragm electromyogram was recorded in the 1st test — with maintaining an inspiratory effort of 30% power for 15 s by 27.9% (p=0.010), 26.1% (p=0.025) and 40.7% (p=0.033) at the 5th, 10th and 15th seconds, respectively, in the 2nd test — with maintaining an inspiratory effort of 50% power for 5 s, by 32.6% (p=0.041) at the 5th second, in the 3rd test — with maintaining an inspiratory effort of 70% power for 5 s, by 42.8% (p=0.009) at the 5th second compared to the control group. At the same time, a more pronounced decrease in the electromyogram frequency was noted in the 1st sample — by 24.2% (p=0.048), 24.7% (p=0.030) compared to the control group, which serves as a sign of fatigue. On the accessory inspiratory muscles, the amplitude increase was higher in patients of the first group compared to the control group, which indicates activation of additional motor units: on the external intercostal muscles in the 1st sample — by 31.7% (p=0.032), 37.9% (p=0.044), in the 2nd sample — by 28.9% (p=0.048), 43.1% (p=0.036); on the sternocleidomastoid muscle in the 1st sample — by 66.1% (p=0.033), 49.4% (p=0.043), in the 2nd sample — by 128.6% (p=0.032).

CONCLUSION: In patients with chronic heart failure stage IIA, surface electromyography using stress tests revealed diaphragm fatigue and increased activity of accessory inspiratory muscles.