Introduction: The respiratory muscle strength regulates the effectiveness of coughing, which clears the airways and protects people from pneumonia. Sarcopenia is an aging-related loss of muscle mass and function, the worsening of which is associated with malnutrition. The loss of respiratory and swallowing muscle strength occurs with aging, but its effect on pneumonia is unclear. This study aimed to determine the risks of respiratory muscle weakness on the onset and relapse of pneumonia in older people in conjunction with other muscle-related factors such as malnutrition. Methods: We conducted a longitudinal study with 47 pneumonia inpatients and 35 non-pneumonia controls aged 70 years and older. We evaluated the strength of respiratory and swallowing muscles, muscle mass, and malnutrition (assessed by serum albumin levels and somatic fat) during admission and confirmed pneumonia relapse within 6 months. The maximal inspiratory and expiratory pressures determined the respiratory muscle strength. Swallowing muscle strength was evaluated by tongue pressure. Bioelectrical impedance analysis was used to evaluate the muscle and fat mass. Results: The respiratory muscle strength, body trunk muscle mass, serum albumin level, somatic fat mass, and tongue pressure were significantly lower in pneumonia patients than in controls. Risk factors for the onset of pneumonia were low inspiratory respiratory muscle strength (odds ratio [OR], 6.85; 95% confidence interval [CI], 1.56-30.11), low body trunk muscle mass divided by height2 (OR, 6.86; 95% CI, 1.49-31.65), and low serum albumin level (OR, 5.46; 95% CI, 1.51-19.79). For the relapse of pneumonia, low somatic fat mass divided by height2 was a risk factor (OR, 20.10; 95% CI, 2.10-192.42). Discussion/Conclusions: Respiratory muscle weakness, lower body trunk muscle mass, and malnutrition were risk factors for the onset of pneumonia in older people. For the relapse of pneumonia, malnutrition was a risk factor.
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