P186 The effect of healthy ageing on human phrenic nerve function

Introduction & objectives Human diaphragm contractility typically declines with advancing age. Associated changes in human phrenic nerve function are less well-investigated. The recent development of multipair oesophageal electrode catheters allows accurate measurement of the latency and amplitude of the crural diaphragm compound muscle action potential (CMAPdi). The principal aim of this study was to investigate the effect of healthy ageing on CMAPdi amplitude and latency using this method. Methods 20 highly active older adults (HAOA, aged 49 to 80 years), and 16 younger adults (YA, age 20 to 35 years), all male, were instrumented with a multipair oesophageal electrode catheter and a dual oesophageal/gastric pressure transducer. Transdiaphragmatic pressure (TwPdi), crural CMAPdi latency and amplitude were measured following left, right and bilateral anterolateral magnetic phrenic nerve stimulation at 100% of maximum stimulator output and compared between the HAOA and YA groups. Maximal inspiratory mouth pressure (PImax), sniff nasal inspiratory pressure (Sniff Pnasal) sniff oesophageal pressure (Sniff Poes) and sniff transdiaphragmatic pressure (Sniff Pdi) were also measured. Results Bilateral TwPdi was significantly lower in HAOA (median (IQR) bilateral TwPdi HAOA 24.8 (22.3 to 35.1) cmH2O) than in YA (bilateral TwPdi YA 31.1 (28.7 to 39.2) cmH2O, p=0.0152). Right TwPdi was significantly lower in HAOA (HAOA 9.8 (9.2 to 11.1) cmH2O, YA 15.2 (13.5 to 18.3) cmH2O, p=0.0005) but differences in left TwPdi did not reach statistical significance (HAOA 11.6 (8.9 to 13.4) cmH2O, YA 15.6 (12.5 to 17.6) cmH2O, p=0.0814). CMAPdi latencies were significantly greater following both left and right phrenic nerve stimulation in HAOA compared to YA (left CMAPdi latency HAOA= 8.9 (8.5 to 9.3) ms, YA=7.5 (7.2 to 8.1) ms,p Conclusions Healthy ageing is associated with increased phrenic nerve latency, interestingly without decrement in motor unit size. Reference ranges of human phrenic nerve function should be updated with age-specific normal values.