THE CONTRACTILE PROPERTIES OF THE ELDERLY HUMAN DIAPHRAGM

It has previously been reported that aging is associated with a substa ntial decrease in diaphragm strength. To test this hypothesis we studi ed 15 (10 male, 5 female) subjects with a mean age of 29 (range 21 to 40) and 15 elderly (10 male, 5 female) subjects, mean age 73 (range 67 to 81). We measured transdiaphragmatic pressure (Pdi) during a maxima l sniff (Sniff Pdi) and during bilateral cervical magnetic stimulation (CMS) of the phrenic nerve roots (Tw Pdi). Additionally in 17 subject s (9 elderly and 8 young) the Pdi elicited by paired CMS (pTw Pdi) was obtained at interstimulus intervals ranging from 10 to 999 ms (1 to 1 00 Hz). There was considerable overlap between groups. Mean Sniff Pdi in the elderly was 119 cm H2O compared with 136 cm H2O for the young s ubjects; this represented a median reduction of 18 cm H2O or 13% (p = 0.05, 95% CI of difference 0 to 33 cm H2O). Mean Twitch Pdi in the eld erly was 26.8 cm H2O compared with 35.2 cm H2O, a median reduction of 8 cm H2O or 23% (p = 0.004, 95% CI 3 to 13 cm H2O). At 10 Hz the elder ly tended to generate a higher fraction of the Pdi obtained at 100 Hz than the young, but this trend did not achieve statistical significanc e (p = 0.11). We conclude that aging is associated with a reduction in diaphragm strength. However the magnitude of the reduction is small a nd may be offset by a leftward shift of the force-frequency relationsh ip.