Effect of preoperative inspiratory muscle training on postoperative outcomes in patients undergoing cardiac surgery: A systematic review and meta-analysis

Table 1 Characteristics of the six included studies

No.	Ref.	Country	Intervention	Control	Intervention group			Control group
					Patients (male: female)	Mean age	Surgery type	Patients (male: female)	Mean age	Surgery type
1	Hulzebos et al[12], 2006	Netherlands	Threshold IMT + incentive spirometry + education in an active cycle of breathing techniques + forced expiration techniques	Usual care (i.e. instruction on deep breathing maneuvers, coughing, and early mobilization) + postoperative incentive spirometry, chest physical therapy, and mobilization scheme	139 (108:31)	66.5 (9.0)	CABG: 139	137 (107:30)	67.3 (9.2)	CABG: 137
2	Savci et al[17], 2011	Turkey	Threshold IMT + mobilization + active exercises of upper and lower limbs + breathing exercises + coughing techniques	Usual care (mobilization, active exercises of upper and lower limbs, breathing exercises, and coughing techniques)	22 (19:3)	62.82 (8.69)	CABG: 22	21 (19:2)	57.48 (11.48)	CABG: 21
3	Moises et al[18], 2014	Brazil	Threshold IMT + breathing exercises + postoperative physical therapy	Guidelines ward routine + postoperative physical therapy	35 (23:12)	58.90 ± 9.53	CABG: 35	35 (29:6)	61.40 ± 8.43	CABG: 35
4	Valken et al[6], 2016	Netherlands	Threshold IMT + incentive spirometry + education (deep breathing maneuvers, coughing, and early mobilization)	Postoperative deep breathing maneuvers, coughing, and early mobilization incentive spirometry and chest physical therapy	119 (93:26)	66 (9.2)	CABG: 99; CABG + valve:20	116 (93:23)	67.5 (9.7)	CABG: 87; CABG + valve: 29
5	Chen et al[19], 2019	China	Threshold IMT + usual care (education coughing, and early mobilization) and abdominal breathing training + postoperative chest physical therapy and mobilization scheme	Threshold IMT [the intensity was fixed at the minimum load of the device (9 cmH2O)] + usual care (education coughing and early mobilization) and abdominal breathing training + postoperative chest physical therapy and mobilization scheme	98 (73:25)	61.68 ± 8.12	CABG: 69; valve: 18; CABG + valve: 11	99 (68:31)	61.68 ± 7.73	CABG: 70; valve: 21; CABG + valve: 8
6	Weber et al[20], 2021	Germany	Threshold IMT + walking below the threshold of subjective exhaustion + mobilization protocol and individual physiotherapy	Postoperative physiotherapy	58 (27:31)	82.2 ± 5.8	TAVR: 58	50 (26:24)	81.7 ± 5.0	TAVR: 50

For threshold inspiratory muscle training, patients must generate a preset pressure to allow airflow for each breath. Once that threshold is achieved, inspiratory flow is not dependent on patient effort. This means that threshold loading is the easiest of these inspiratory muscle training methods to standardize and prescribe for patients. CABG: Coronary artery bypass grafting; IMT: Inspiratory muscle training; TAVR: Transcatheter aortic valve replacement.