Page 135 - Biomedical Engineering and Design Handbook Volume 1, Fundamentals

112 BIOMECHANICS OF THE HUMAN BODY

TABLE 5.1 Summary of Averaged Values of Maximal Mouth Pressure of Normal Subject
Male Female
P (cmH O) P (cmH O) P (cmH O) P (cmH O)
I 2 E 2 I 2 E 2
Reference No. & sex RV FRC FRC TLC RV FRC FRC TLC
Cook et al., 37M 11F 124 ± 30 103 ± 20 100±40 190±45 102±20 87±25 57±22 146±30
1964
Black and 120 107 ± 35 208±76 74±30 168±44
Hyatt, 1969
Rochester and 80M 121F 127 ± 28 216±45 91±25 138±39
Arora, 1983
Wilson et al., 48M 87F 106 ± 31 148±34 73±22 93±17
1984
Chen and 80M 80F 104± 25 90 ± 25 115±33 132±38 74±21 65±18 75±20 88±25
Kuo, 1989
McElvaney 40M 64F 108± 26 173±41 75±24 115±34
et al., 1989
Leech et al., 300M 480F 115 ± 35 160 ±40 70 ±28 93±33
1983
Nickerson and 15 M + F 122± 8
Keens, 1982
Ambrosino 22 M + F 104± 28 142±33
et al., 1994
McParland 9 M+F 70–150 70–120 70–200 100–230
et al., 1992
Ratnovsky 6 M+F 89± 16 73 ± 14 81±28 109±19
et al., 1999
+/− represents the SD.

(Laghi and Tobin, 2003; Ratnovsky et al., 2006). Measurement of maximal inspiratory and expiratory
mouth pressure at different lung volumes in untrained but cooperative subjects revealed a reduction in
expiratory muscle strength as lung volume decreases from TLC and in inspiratory muscles as lung
volume increases from RV (Ratnovsky et al., 1999).
Measurement of sniff nasal inspiratory pressure is another method to assess the global strength
of respiratory muscles. The nasal pressure is measured in an occluded nostril during a maximal sniff
performed through the contralateral nostril from FRC. This pressure closely reflects esophageal pres-
sure, and thus, inspiratory muscle strength (Fauroux and Aubertin, 2007; Fitting, 2006; Stefanutti
and Fitting, 1999; Steier et al., 2007).

5.3.2 Endurance of the Respiratory Muscles
The ability of a skeletal muscle to endure a task is determined by the force of contraction, the duration
of contraction, and the velocity of shortening during contraction. The endurance capacity of respiratory
muscles depends on lung volume (which determines muscle length), velocity of muscle shortening, and
type of breathing maneuver used in the test (Rochester, 1988). Maximal voluntary ventilation (MVV)
is the oldest test of respiratory muscle endurance in which the level of ventilation that can be sustained
for 15 minutes or longer is measured. Besides the forces required for reaching this high level of venti-
lation, this test reflects the ability of the respiratory muscles to reach and sustain the required
contractile output (Freedman, 1970).
The two most popular methods to measure respiratory muscle endurance are the resistive and the
threshold inspiratory load (Fiz et al., 1998; Hart et al., 2002; Johnson et al., 1997; Martyn et al.,
1987; Reiter et al., 2006). The incremental threshold loading is imposed during inspiration through