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Patients with traumatic quadriplegia or progressive neuromuscular conditions may require long-term ventilatory support that is most frequently managed by intubation and subsequent tracheostomy and tra­cheostomy intermittent positive pressure ventilation (TIPPV) with an inflated cuff. Patients are often unnecessarily maintained with an inflated cuff longer than necessary. Although cuff deflation and transition to the use of cuffless tracheostomy tubes have been described during ventilator weaning of patients with paralytic respiratory insufficiency, weaning from TIPPV is not always possible. There is often no effort made to optimize the tracheostomy tube diameter and the delivered volumes to permit cuff deflation or removal and there appear to be no guidelines in the literature to facilitate this.

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All measurements in the present study showed excellent reproducibility, and deviation for each device under the same conditions was within 3 percent of the coefficient of variance. Standard deviation was very small and for all experimental conditions all values were statistically significant except comparison for different pressure-monitoring sites of Vapoi-Phase.

Thedl(-)

Figure 3 shows dl( —) for each device for four different inspiratory flow rates and Paw monitoring at three different sites. All devices exhibited the largest dl( —) when the pressure monitoring was done at PI. The dl( —) was smallest when the pressure was mon­itored at P2 under inspiratory flow rates of 30 and 60 L/min and all humidifiers had little effect on dl( —). Under a high inspiratory flow rate, dl( —)P3 of the HWB systems was less than dl( —)P2. The reason for this phenomenon was not clear. As the inspiratory flow rate increased, dl(-), especially dl( —)P1, of all devices increased. The cascade humidifier exhibited the largest dl( — )P1 at any inspiratory flow rate. Vapor- Phase (Inspiron) represented almost no resistance to gas flow and its dl( —) was zero. When Paw was monitored at P3, dl( —) for HME was greater than that of HWB.

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Endotracheal intubation results in a bypass of the natural warming and humidifying process through the nasopharynx, and a humidifying device is therefore necessary during respiratory tract manage­ment. Although FDA guidelines place some require­ments on the flow-resistance characteristics of humid­ifiers at continuous flow rates, there have been few reports investigating the flow-impedance characteris­tics of humidifiers under dynamic conditions and the changes in respiratory work load due to humidifiers. In the present study, we calculated the amount of AWL imposed by different types of humidifying de­vices and evaluated their flow-impedance character­istics. In addition to this, we examined the ventilator factors which affect the values of AWL.

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The results of our study indicate that the use of long-term oxygen via nasal cannulas in this group of subjects with COPD did not impair their sense of smell or taste. Even though significant differences were noted in the basic smell and taste test scores in all subjects with COPD as compared with controls, there was no difference between subjects with COPD with oxygen and subjects with COPD without oxygen.

In subjects with COPD with oxygen (group 1), no differences were noted in the smell and taste test scores with or without oxygen via nasal cannulas, suggesting no sensory effect of nasal cannulas on smell and taste. Given the lack of an effect of nasal cannulas itself, it was possible to use these data to obtain a measure of test-retest reliability. The correlation for smell and taste was 0.85 and 0.75, respectively, indicating good test-retest reliability for both smell and taste. The data for smell compared favorably with those of Doty et al (r= .91).

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Demographics

Demographics of the study subjects are shown in Table 1. Age and sex were equally matched in all three groups. Subjects with COPD who were receiving oxygen had more severe obstructive lung disease as compared with subjects with COPD who were not receiving oxygen. Of the 20 subjects with COPD receiving oxygen, 17 were receiving continuous oxygen and three received only nocturnal oxygen.

Smoking status was variable. Only eight subjects were current smokers, 19 were nonsmokers, and the remaining 33 were exsmokers. Two measures of smok­ing were obtained: (1) mean pack years each subject had smoked and (2) number of years since quitting smoking. Mean pack years was the highest for group 1, with significant differences between the three groups. In order not to exclude the 19 nonsmokers from the analysis, they were arbitrarily equated with those who had quit 30 years ago, about the maximum observed in this group of subjects. With this assump­tion, years since quitting was not different between group 1 and 2, but both groups were significantly different than control group 3 (Table 2).

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