SUMMARY1. The cardiovascular effects of an acute haemorrhage (2 % of the body weight)were studied over a 60 min period in three groups of rats: (a) Brattleboro rats with hereditary hypothalamic diabetes insipidus (b.d.i.) lacking circulating vasopressin, (b) control rats of the parent Long Evans (l.e.) strain, and (c) l.e. rats treated with an antagonist of the vascular action of vasopressin.2. Prior to the haemorrhage there were no significant differences between the three groups of rats with respect to mean arterial blood pressure, cardiac output, stroke volume or total peripheral resistance.3. Following the haemorrhage cardiac output and stroke volume were severely reduced in all three groups of rats. Total peripheral resistance was relatively unaffected in antagonist-treated l.e. rats and b.d.i. rats, but rose substantially in response to the loss of blood in the control l.e. group. Both total peripheral resistance and mean arterial blood pressure were markedly greater in the untreated l.e. control rats than in the other two groups of animals during the first 20 min after haemorrhage.4. The mean heart rate measured in Brattleboro rats was elevated compared with that of control l.e. rats throughout the experiment and, in addition, significantly greater than that of antagonist-treated l.e. rats during the first 40 min after the haemorrhage.5. Survival rate for the b.d.i. rats following the 2 % haemorrhage was lower than that for l.e. control rats and antagonist-treated l.e. rats.6. The results indicate that the recovery of the blood pressure following an acute arterial haemorrhage is significantly influenced by vasopressin, particularly during the first 20 min, and that the predominant effect of the hormone is to increase the total peripheral resistance. The higher mortality associated with volume depletion in the b.d.i. rats is unlikely to be directly related to the absence of the vascular action of vasopressin, since administration of the vasopressin antagonist to normal l.e. rats does not reduce their survival rate.

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Introduction: Continuous positive airway pressure (CPAP) remains the treatment of choice for obstructive sleep apnea (OSA). Although it is an effective treatment, adherence is poor. The literature has failed to identify treatment variables that consistently predict CPAP adherence. Methods: We performed a retrospective analysis of patients with OSA started on CPAP in our clinic over the past 7 years. We compared those who were compliant after 30 days of CPAP use with those who did not demonstrate regular use, defined as CPAP use for ≥4 hours per night on 70% of nights. We assessed several clinical and demographic variables for their relationship with CPAP adherence including self-identified race, gender, sedative-hypnotic use during the diagnostic polysomnogram, mask type and brand. Differences between the groups were determined through the Chi-square test and Fisher's Exact test. Results: Two-thousand and four patients were included in the analysis (91% men, mean age 45.2 years ±10.8, mean AHI of 19.79 ± 15.1, mean BMI of 29.49 ± 8.7). At 30 days following the initiation of CPAP therapy, overall compliance was 66%. Patients treated with a full face mask (56.6%) were significantly more compliant (68.2%) compared to those using a nasal interface (63.5%; p-value of 0.032, OR 1.2). In regards to the different mask brands, there was no statistical significance between the six separate interfaces included in the database. Selfidentified Asian patients (2%) were also more likely to be compliant (77.8%; p-value of 0.000, OR 2.9) compared to other categories of race. The use of a sedative hypnotic, eszopiclone or zolpidem, during the polysomnogram was not indicative of compliance (p-value of 0.887). Conclusion: Our study demonstrates a statistically superior CPAP compliance at 30 days amongst patients treated with full face masks. Although statistically significant, these findings are not felt to be clinically relevant. However, this contradicts previously published data that full face masks negatively affect CPAP adherence. Additional investigation is warranted to further identify treatment variables associated with improved CPAP compliance. Support (If Any)

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