Sleep Apnea and Resistant Hypertension: When the Blood Pressure Problem Happens at Night

Key Takeaways:

• In a systematic search for secondary causes among 125 patients with resistant hypertension, obstructive sleep apnea was the most common associated condition, found in 64 percent, far ahead of primary aldosteronism at 5.6 percent.
• In people with obstructive sleep apnea, blood pressure and sympathetic nerve activity do not fall during sleep as they should; mean pressure climbed from 92 mm Hg awake to 116 mm Hg in stage II sleep and 127 mm Hg in REM sleep, and sympathetic activity stayed high even during the day.
• In the HIPARCO trial of 194 patients taking an average of 3.8 blood pressure medications, 12 weeks of CPAP lowered 24-hour mean blood pressure by 3.1 mm Hg and 24-hour diastolic pressure by 3.2 mm Hg compared with no CPAP, and the benefit grew with nightly hours of use.

When blood pressure stays high despite three or more medications at good doses, the usual reflex is to add a fourth. The better first move is to look at the night, because the link between sleep apnea and resistant hypertension is one of the tightest in cardiovascular medicine. In obstructive sleep apnea the airway collapses repeatedly during sleep. Each event lowers oxygen and raises carbon dioxide, and the carotid body chemoreceptors answer with a burst of sympathetic nerve traffic that clamps down the arterioles just as the airway snaps open. When investigators recorded nerve activity directly in people with sleep apnea, sympathetic output peaked at the end of each apneic event, and mean blood pressure rose from 92 mm Hg awake to 116 mm Hg in stage II sleep and 127 mm Hg in REM sleep, instead of falling as it does in healthy sleepers. The effect did not stay in the bedroom. Sympathetic activity was elevated even when these patients were awake, which means the night shift of repeated alarms resets the daytime baseline. CPAP, by holding the airway open, reduced both nerve activity and blood pressure during sleep.

The prevalence numbers explain why this belongs on every resistant hypertension checklist. In a university hypertension clinic, overnight sleep studies in 41 adults on three or more drugs found obstructive sleep apnea in 83 percent, most of it previously unrecognized, and it was both more common and more severe in men. A larger Brazilian study then went looking systematically for every known secondary cause of hypertension in 125 consecutive patients with resistant hypertension, testing everyone regardless of symptoms. Obstructive sleep apnea of at least moderate severity was the most common condition, present in 64 percent. Primary aldosteronism, the cause most clinicians think of first, came in at 5.6 percent, and renal artery stenosis at 2.4 percent. Three simple bedside features predicted who had apnea: age over 50, a large neck circumference, and snoring. None of these patients needed daytime sleepiness to qualify, and many people with apnea-driven hypertension do not feel especially tired, which is exactly why it goes undiagnosed.

How much does treating sleep apnea lower resistant hypertension?

Honestly, less than people hope, and more than nothing. The HIPARCO trial randomized 194 Spanish patients with resistant hypertension and at least moderate sleep apnea, who were taking an average of 3.8 antihypertensive drugs, to CPAP or no CPAP while keeping their medications unchanged. After 12 weeks, the CPAP group’s 24-hour mean blood pressure fell 3.1 mm Hg more than the control group’s, and 24-hour diastolic pressure 3.2 mm Hg more; the difference in 24-hour systolic pressure did not reach statistical significance. The normal nighttime dip in pressure returned in 35.9 percent of CPAP users versus 21.6 percent of controls, and the more hours a night people wore the mask, the more their pressure fell. A 2021 meta-analysis of 10 randomized trials in 606 patients found CPAP lowered 24-hour systolic pressure by about 5 mm Hg and diastolic by about 4 mm Hg, with the clearest effect at night. Those are modest numbers, and CPAP is not a replacement for medication. But it treats a driver rather than a reading, it improves sleep itself, and it works only if it is worn. For anyone whose pressure will not come down, especially with snoring, a thick neck, or witnessed pauses in breathing, a home sleep test is a reasonable next step before a fourth or fifth pill.

References:

1. Somers, V. K., Dyken, M. E., Clary, M. P., & Abboud, F. M. (1995). Sympathetic neural mechanisms in obstructive sleep apnea. The Journal of Clinical Investigation, 96(4), 1897-1904.
2. Logan, A. G., Perlikowski, S. M., Mente, A., Tisler, A., Tkacova, R., Niroumand, M., et al. (2001). High prevalence of unrecognized sleep apnoea in drug-resistant hypertension. Journal of Hypertension, 19(12), 2271-2277.
3. Pedrosa, R. P., Drager, L. F., Gonzaga, C. C., Sousa, M. G., de Paula, L. K., Amaro, A. C., et al. (2011). Obstructive sleep apnea: the most common secondary cause of hypertension associated with resistant hypertension. Hypertension, 58(5), 811-817.
4. Martínez-García, M. A., Capote, F., Campos-Rodríguez, F., Lloberes, P., Díaz de Atauri, M. J., Somoza, M., et al. (2013). Effect of CPAP on blood pressure in patients with obstructive sleep apnea and resistant hypertension: the HIPARCO randomized clinical trial. JAMA, 310(22), 2407-2415.
5. Labarca, G., Schmidt, A., Dreyse, J., Jorquera, J., Enos, D., Torres, G., et al. (2021). Efficacy of continuous positive airway pressure (CPAP) in patients with obstructive sleep apnea (OSA) and resistant hypertension (RH): Systematic review and meta-analysis. Sleep Medicine Reviews, 58, 101446.