Atrial natriuretic peptide: physiological release associated with natriuresis during negative pressure breathing in man

The impact of sleep apnoea syndrome on nocturia according to age in men

Study Type--Symptom prevalence (cohort) Level of Evidence 2b. What's known on the subject? and What does the study add? Sleep apnoea syndrome (SAS) can be a risk factor for nocturia, although whether the relationship between nocturia and SAS changes according to age remains to be addressed. SAS has a modest impact on nocturia frequency and the prevalence of pathological nocturia in young adults and middle-aged men. However, SAS may not be a risk factor for nocturia in the elderly, and age-related urinary diseases and voiding dysfunctions could over-ride the influence of SAS on nocturia in the elderly.

OBJECTIVE

• To assess the association between nocturia and sleep apnoea syndrome (SAS) according to age, as well as to determine the factors related to nocturia.

PATIENTS AND METHODS

• A total of 1757 men who had been referred to a sleep laboratory underwent polysomnography. • Nocturia frequency was assessed using a questionnaire, and pathological nocturia was defined as the need to void two or more times per night. • The Pittsburgh Sleep Quality Index (PSQI) and Beck Depression Inventory (BDI) were applied to all study subjects.

RESULTS

• Nocturia frequency was significantly correlated with age (r = 0.405, P < 0.001) and the apnoea-hypopnoea index (AHI) (r = 0.065, P < 0.01). • In those men aged <65 years, significant correlations were found between nocturic frequency and age, AHI, BDI and PSQI. • Multiple regression analysis showed that age (β = 0.303, P < 0.001), AHI (β = 0.107 P < 0.001) and benign prostatic hypertrophy (BPH; β = 0.069, P < 0.01) were associated with nocturia, and that the presence of pathological nocturia was predicted by BPH (odds ratio [OR], 2.77; P < 0.01), age (OR, 1.09; P < 0.001) and AHI (OR, 1.02; P < 0.001). • However, in men aged >65 years, nocturia frequency was significantly associated with BDI and PSQI, although no relationship was found between nocturia frequency and SAS parameters. • BPH was more frequently observed in elderly men with pathological nocturia than in those without pathological nocturia (OR, 2.18; P < 0.05).

CONCLUSIONS

• In the elderly, SAS may not be a risk factor for nocturia. • Age-related urinary diseases and voiding dysfunction may over-ride the influence of SAS.

Quantitating nocturia: a study into the recording of solute and water excretion to determine causation

BACKGROUND

Nocturia is common but the clinical assessment of its severity and cause rarely involves any biochemical analysis. Investigating the cause of nocturia needs to be informed by the overall 24 h fluid and solute excretion patterns. The aim of this study was to establish a practical method of monitoring the renal excretion of water and solutes over a complete 24 h cycle.

METHODS

The excretion patterns of sodium, volume and osmoles were assessed in 89 healthy control subjects over a 24 h period by sampling each voiding from the 24 h collection and then using the total urine creatinine as the denominator. A group of 21 patients under investigation for sleep-disordered breathing (SDB: a group of disorders known to increase the risk of nocturia) were also studied to determine comparative excretion patterns.

RESULTS

Reference excretion patterns of sodium, volume and osmoles were described. Patients under investigation for SDB had overall a significant (P < 0.001) increase in urine sodium excretion at night (nocturnal natriuresis) matched by an increased osmotic excretion and accompanied by a significantly increased nocturnal urine volume (P < 0.001).

CONCLUSION

Breaking down a 24 h urine collection into voided aliquots provides practical information on the pattern of water and solute excretion. Such patterns may assist in identifying the underlying mechanism of significant nocturia in individual patients presenting with this symptom, and could be used as a method of monitoring treatment.

Nocturia and snoring: predictive symptoms for obstructive sleep apnea

PURPOSE

Current screening for obstructive sleep apnea (OSA) emphasizes self-reported snoring and other breathing symptoms. Nocturia, a symptom with a precise pathophysiological link to sleep apnea, has not been assessed as a screening tool for this common disorder of sleep respiration. In a large sample of adults presenting to area sleep centers, we aimed to determine the predictive power of nocturia for OSA and compare findings with other markers of OSA commonly used to screen for this disease.

METHODS

This was a retrospective chart review. A consecutive sample of 1,007 adult patients seeking treatment at two sleep centers in New Mexico completed detailed medical and sleep history questionnaires and completed diagnostic polysomnography testing. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of nocturia, snoring, high body mass index, sex, and age for OSA were determined. Hierarchical linear regression determined unique variance contribution to the apnea-hypopnea index, the objective measure of sleep apnea severity.

RESULTS

The results are as follows: sensitivities--snoring, 82.6% and nocturia, 84.8%; specificities--snoring, 43.0% and nocturia, 22.4%; PPVs--snoring, 84.7% and nocturia, 80.6%; and NPVs--snoring, 39.6% and nocturia, 27.9%. With hierarchical linear regression, patient-reported nocturia frequency predicted apnea-hypopnea index (OSA severity) above and beyond body mass index, sex, age, and self-reported snoring (P<0.0001).

CONCLUSIONS

Nocturia appears comparable to snoring as a screening tool for OSA in patients presenting to a sleep medical center. Research in urology and primary care clinics is needed to definitively clarify the use of nocturia as a screening instrument for obstructive sleep apnea.

Sleep disordered breathing and nocturnal polyuria: nocturia and enuresis

Although nocturnal voiding is frequently attributed to urologic disorders, nocturia and enuresis are also important symptoms of sleep-disordered breathing. However, polyuria can be elicited by obstructive sleep apnea as well as bedrest, microgravity and other experimental conditions where the blood volume is shifted centrally to the upper body. The nocturnal polyuria of sleep apnea is an evoked response to conditions of negative intrathoracic pressure due to inspiratory effort posed against a closed airway. The mechanism for this natriuretic response is the release of atrial natriuretic peptide due to cardiac distension caused by the negative pressure environment. This cardiac hormone increases sodium and water excretion and also inhibits other hormone systems that regulate fluid volume, vasopressin and the rennin-angiotensin-aldosterone complex. Treatment of sleep apnea and airway compromise has been shown to reverse nocturnal polyuria and thereby reduce or eliminate nocturia and enuresis. Thus, careful evaluation of nocturia and enuresis for evidence of nocturnal polyuria can increase the diagnostic certainty of referring primary care providers and sleep specialists. In addition, the resolution of these bothersome symptoms after treatment can contribute to patient satisfaction as well as reinforce treatment compliance.

Nocturnal polyuria in type 2 diabetes: a symptom of obstructive sleep apnea

PURPOSE

Polyuria and nocturia in individuals with type 2 diabetes may be due to obstructive sleep apnea (OSA), a recently recognized etiology of excess nighttime urine production. This exploratory study examined the relationships among glucose control, OSA, and nocturnal urine production.

METHODS

A sample of community-dwelling older adults (20 nondiabetic subjects and 10 poorly controlled type 2 diabetes subjects) was recruited based on self-report of nocturia more than twice per night. Participants were monitored on a metabolic research unit for 24 hours to track intake/output, collect blood and urine samples, and conduct an overnight polysomnography sleep study.

RESULTS

None of the subjects had fasting serum glucose levels above the renal threshold. OSA was found in 65% of subjects. Those with moderate/severe OSA had significantly greater overnight urine production than subjects without OSA. Subjects with type 2 diabetes and moderate/severe OSA had the highest nocturnal urine production.

CONCLUSIONS

The high incidence of undetected OSA in subjects with type 2 diabetes with nocturia suggests that nocturia, OSA, and type 2 diabetes frequently coexist and may be interrelated.

Mechanism of atrial natriuretic peptide release with increased inspiratory resistance

Elevated plasma atrial natriuretic peptide (ANP) levels and concomitant increases in renal sodium and water excretion are often encountered in respiratory diseases associated with increased airway resistance such as obstructive sleep apnea. The present study utilized an anesthetized rat model to determine the principal mechanism(s) responsible for stimulation of ANP release in this clinical syndrome. A 10-minute increase in external resistive loading, which reduced peak tracheal pressure to -15 to -17 mm Hg produced a significant increase in both central venous pressure and right atrial transmural pressure. This maneuver subsequently resulted in significant transient increases in glomerular filtration rate; urine flow; urinary Na+, K+, and Cl- excretion; and urinary cyclic guanosine monophosphate (cGMP) excretion, which was taken as an index of increased circulating levels of ANP. Similar changes in renal function and cGMP excretion occurred when arterial PO2 was lowered to a degree equivalent to that seen with increased resistive loading. Lowering arterial PO2 also significantly increased mean central venous pressure and right atrial transmural pressure. Conversely, the resistive loading-induced changes in renal function and cGMP excretion did not occur when the reduction in arterial PO2 was prevented by breathing a high O2 gas mixture during the resistive loading. Additionally, O2 supplementation prevented the increases in both mean central venous pressure and right atrial transmural pressure caused by increased resistive loading. These data indicate that the elevated ANP release that results from an acute increase in external resistive loading is not caused by a decrease in intrathoracic pressure but rather suggest that the elevated ANP release is primarily caused by an increased right atrial transmural pressure resulting from hypoxia-induced pulmonary vasoconstriction.

Neuroendocrine changes in chronic cardiac failure

Numerous hormonal and neuroendocrine changes have been described in patients with chronic cardiac failure. These affect the balance of vasodilator and vasoconstrictor factors in favour of the latter, to the detriment of the circulation. Whether this is a reaction to central cardiac (haemodynamic) abnormalities, or is an integral part of the syndrome of heart failure, remains to be determined. Catecholamine levels are increased, especially in severe heart failure, and contribute to the vasoconstriction and probably also to lethal ventricular arrhythmias. The renin-angiotensin-aldosterone system (RAAS) is also activated, causing fluid retention and further vasoconstriction. In the earlier stages, some of this increase may be iatrogenic due to the use of loop diuretics or inhibitors of angiotensin converting enzyme, but there is evidence for independent RAAS activation in more severe grades of heart failure. The role of vasoconstrictor peptides such as neuropeptide Y and endothelin is briefly considered. Counterbalancing these are vasodilator peptides, in particular atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP). The possibility of therapeutic interventions to increase circulating natriuretic hormone levels is discussed.

[Atrial natriuretic factor]

Although ANF research started 30 years ago, the atrial natriuretic factor (ANF) was only discovered recently (1981). The presence of such a factor has been suspected for many years because of histological and physiological arguments. In 1956, Kish found "dense granules" in the atrial walls of guinea pigs. Gauer and Henry could explain some of their experimental results on diuresis and natriuresis only by suggesting the presence of a third hormonal factor, but neither by the renin-angiotensin system, nor the anti-diuretic hormone. Hall et al. were the first to recognize a link between the granules and water and sodium metabolism. But it was De Bold who published the crucial experiment in 1981: injecting right atrial extracts to anaesthetized rats rapidly induced intense and transitory diuresis and natriuresis. ANF was born, and, at the same time, the concept of the heart as an endocrine gland. Indeed, ANF corresponds to the strict definition of a hormone. It has the following properties: natriuresis and diuresis via an increase in glomerular filtration fraction without any major changes in renal plasma flow; direct vasodilation of the large arteries with only few effects on small arterioles and veins. The stimuli for ANF secretion are mechanical and pharmacological, especially drugs currently used by anaesthetists. Atrial distension is the main mechanical stimulus. An increase in atrial transmural pressure is always followed by a release in ANF, but this effect is not constant for increases in intra-luminal pressure. It is the former pressure gradient alone that reflects the volume of the right atrium, the mechanical stimulus for ANF secretion. Tachycardia, or, more precisely, an increase in the atrial contraction rate, also leads to an important release of ANF. Cardiac nerves are not necessary for this, as demonstrated by studies in heart transplant patients. Only few pharmacological agents have been shown to really stimulate ANF secretion. In rats, morphine has a direct secretory effect, whereas ketamine hydrochloride, diethylether and chloral hydrate do so by increasing the release of catecholamines. The effects of alpha, beta adrenergic agonists and calcium agonists remain controversial. ANF, which has diuretic and vasodilator effects, plays a part, together with the renin-angiotensin system and the anti-diuretic hormone, in blood volume control in mammals. However, it has a special role to play, because it is a rapid release hormone: rapid vascular filling leads to an increase in ANF in less than 1 minute, with a parallel increase in diuresis.