[Diaphragmatic reserve strength in obese patients]

Nine obese patients (OB) and seven normal subjects (N) were studied in order to determine diaphragmatic strength reserve, measured in terms of diaphragm Tension/Time Index (TTdi). This index was measured with the patients awake and during the obstructive apnea (OA) episodes. TTdi was 2.7 times superior in the OB (p < 0.0005) and was related with a lower Pdi Max (102 vs 202 cm H2O; p < 0.005) and with a higher Pdi (9 vs 6 cm H2O; p < 0.05). During OA the TTdi was higher than the threshold value to develop diaphragmatic fatigue (0.15-0.20) in three patients. This value was not exceeded in one patient because of striking paradoxical diaphragmatic movements. As for anthropometric data, DPI% range was higher and wider in OB (Table 1). The pCO2 in OB was 40 +/- 6 mmHg. In all patients (Table 3), severe hypoxia and hypercapnial were observed. TTdi evolution in an OA in 4 patients can be appreciated in Figure 3. It can be concluded that the diaphragmatic strength reserve is reduced in OB so that they are more susceptible to develop diaphragmatic fatigue. A fatigant respiratory pattern was also registered during the OA.