Correlation between respiratory muscle weakness and frailty status as risk markers for prognosis in patients with cardiovascular disease
Authors: Hamazaki N , Kamiya K , Nozaki K , Ichikawa T , Yamashita M , Uchida S , Tabata M , Maekawa E , Yamaoka-Tojo M , Matsunaga A , Ako J 
Published: November 2020

Abstract

Background
Respiratory muscle weakness (RMW), frequently observed in patients with cardiovascular disease (CVD), is documented as a predictor for exercise intolerance and poor prognosis. On the other hand, frailty is commonly associated with disease condition, leading to increased risk of morbidity and mortality. Although the developmental mechanism of RMW and frailty is partly similar, the relationship between these statuses remains unclear.

Purpose
We aimed to investigate the correlation between RMW and frailty and its impact on prognosis in patients with CVD.

Methods
We studied 771 consecutive patients (68.5±13.1 years, 256 females) who were hospitalized for CVD treatment and underwent cardiac rehabilitation during hospitalization. Patients who received thoracic surgery within the last 3 months or could not perform respiratory function test were excluded from this study. As patient characteristics, we obtained body mass index, comorbidity conditions, smoking history, blood examinations, echocardiographical variables, and lung function from medical database. The frailty status on admission was assessed using frailty score consisting of 5 items including gait speed, nutrition/shrinking, physical activity, forgetfulness, and emotions/exhaustion, and patients who had 3 items were defined as frailty. We also measured maximal inspiratory pressure (PImax) as respiratory muscle strength at hospital discharge, and RMW was defined with PImax &lt;70% of predicted value. Primary end-point was all-cause clinical events including all-cause death and/or unplanned readmission after hospital discharge. We examined the prevalence of RMW and frailty and the correlation between these statuses. The relationships of RMW with the clinical events for each presence or absence of frailty were also investigated using multivariate Cox proportional hazard models.

Results
RMW and frailty were defined in 163 (33.5%) and 126 (28.7%) patients, respectively, and 95 patients (12.4%) among them showed an overlap of both statuses (Figure 1). Frailty was detected as a significant indicator of RMW after adjusting for confounding factors (adjusted odds ratio: 1.57, 95% CI: 1.12–2.19, P=0.009). Over the median follow-up periods of 1.2 years, all-cause clinical events occurred in 154 patients (20.0%). RMW was significantly and independently associated with increased incidence of all-cause clinical events in patients with both non-frailty (adjusted hazard ratio [HR]: 1.64, 95% CI: 1.09–2.46, P=0.017) and frailty (adjusted HR: 1.97, 95% CI: 1.14–3.42, P=0.015) even after adjusting for clinical confounding factors (Figure 2).

Conclusions
This study is the first to demonstrate that RMW correlated to frailty in patients with CVD, and 12.4% of patients had overlap status. Moreover, RMW was significantly associated with an increased risk of all-cause clinical events in patients with CVD and frailty.

Funding Acknowledgement
Type of funding source: Public grant(s) – National budget only. Main funding source(s): Japan Society for the Promotion of Science Grant-in-Aid