To the best of our knowledge, this is the first study that focused on the NC in patients with ICH. We found that NC was an independent risk factor for poor prognosis of ICH, and BMI was independently inversely associated with poor outcome in ICH patients. NC is an indicator of obesity that reflects human health [16–21]. Previous studies have shown that NC is associated with an increased risk of hypertension , diabetes [17, 21] and metabolic syndrome . NC is also found to be associated with congestive heart failure incidence and coronary heart disease mortality . However, researches regarding the association between NC and ICH were limited.
According to the “obesity paradox”, obese and overweight stroke patients had favorable prognosis than those with a normal or lower BMI [22–24]. Consistent with these findings, we found that BMI was independently inversely associated with poor outcome in ICH patients. Interestingly, we also found a contradictory relationship between BMI and NC in predicting the prognosis of ICH. One possible explanation for the paradoxical phenomenon may be that the two obesity indicators are different in fat distribution. BMI only reflects the total body obesity and NC represents an alternative method for measuring upper body subcutaneous fat . Moreover, it had been demonstrated that NC was associated with oropharyngeal fatty infiltration, which narrows the upper airway, resulting in obstructive sleep apnea (OSA) .
A retrospective study found that the larger the NC (≥ 43.2 cm in men and ≥ 36.8 cm in women), the higher the incidence of obstructive sleep apnea was 2.52 times in men and 3.13 times in women . And, it was reported that compared with BMI, NC better explained the change in apnea-hypopnea index in morbidity obese women (n = 115) in the predictive model . OSA had been reported to be associated with ICH. The hypoxia and hemodynamic responses associated with OSA may predispose to stroke . Moreover, OSA was associated with the development of perihematoma edema , which may cause poor outcome after ICH [30–32]. Several mechanisms may have influence on the development of encephaledema after ICH. The early stage of cerebral edema occurs in the first few hours after ICH, which involves hydrostatic pressure induced by formation of hematoma and retraction of clot, the second phase, caused by production of thrombin and activation of the coagulation cascade, occurs within the first 24 hours, and the delayed stage involves in red blood cells hemolysis and hemoglobin-induced toxicity [33, 34]. The sizes of perihematoma edema have also been related to several factors such as the level of serum ferritin and increased matrix metalloproteinase-9 activity, which is an important enzyme for the blood brain barrier remodeling and perihematoma edema development [35–38].
Due to a momentary cessation of breathing, OSA patients with this disorder have repeated episodes of hypoxia/reoxygenation, promoting systemic oxidative stress, clotting cascade activation, inflammation, and damaged repair competence of the vascular endothelium . Thus, through the above several pathways, OSA may have a role in the generation of perihematoma edema. Moreover, OSA has also been demonstrated to be associated with the enhanced activity of matrix metalloproteinase-9. Therefore, it is reasonable to believe that the association between OSA and perihematoma edema is biologically plausible.
Mechanical ventilation after tracheotomy or endotracheal intubation may prevent OSA-related hypoxia. However, a previous study have reported that in acute spontaneous ICH patients, endotracheal intubation and mechanical ventilation were associated with increased risk of hospital-acquired pneumonia and in-hospital mortality . Consistently, in the present study, we found that the proportions of patients with tracheotomy and endotracheal intubation were higher in the poor outcome group. The reason may be that the hematoma volume in ICH patients with tracheotomy or endotracheal intubation was larger than patients without tracheotomy or endotracheal intubation, which suggested more severe condition and poorer prognosis.
In addition, previous studies have shown that NC was associated with an increased risk of hypertension , diabetes [17, 21] and metabolic syndrome , which also played a role in the occurrence and development of ICH [41–43]. Furthermore, Pezzini et al. found that obesity, mainly through its indirect effect on hypertension and obesity-related complication, played a role in ICH . Taken together, NC should not be overlooked in evaluating ICH patients.
However, our study still has several limitations. First, this study collected data from one hospital, with a limited sample size, which may lead to selection bias. Second, NC is one of the factors causing upper respiratory tract stenosis, and the presence of other unmeasured factors will still influence our final conclusion. Third, OSA was not accurately assessed in our study. At last, all the ICH patients were only from West China Hospital, recruiting poor clinical conditions patients usually because of the medical referral system.