Beneficial Effects of Nitric Oxide on Outcomes after Cardiac Arrest and Cardiopulmonary Resuscitation in Hypothermia-treated Mice

Abstract

Background Therapeutic hypothermia (TH) improves neurological outcomes after cardiac arrest (CA) and cardiopulmonary resuscitation (CPR). Although nitric oxide prevents organ injury induced by ischemia and reperfusion, role of nitric oxide during TH after CPR remains unclear. Here, we examined the impact of endogenous nitric oxide synthesis on the beneficial effects of hypothermia after CA/CPR. We also examined whether or not inhaled nitric oxide during hypothermia further improves outcomes after CA/CPR in mice treated with TH. Methods Wild-type (WT) mice and mice deficient for nitric oxide synthase 3 (NOS3−/−) were subjected to CA at 37°C and then resuscitated with chest compression. Body temperature was maintained at 37°C (normothermia) or reduced to 33°C (TH) for 24 hours after resuscitation. Mice breathed air or air mixed with nitric oxide at 10, 20, 40, 60, or 80 ppm during hypothermia. To evaluate brain injury and cerebral blood flow, magnetic resonance imaging was performed in WT mice after CA/CPR. Results Hypothermia up-regulated the NOS3-dependent signaling in the brain (n=6–7). Deficiency of NOS3 abolished the beneficial effects of hypothermia after CA/CPR (n=5–6). Breathing nitric oxide at 40 ppm improved survival rate in hypothermia-treated NOS3−/− mice (n=6) after CA/CPR compared to NOS3−/− mice that were treated with hypothermia alone (n=6, P<0.05). Breathing nitric oxide at 40 (n=9) or 60 (n=9) ppm markedly improved survival rates in TH-treated WT mice (n=51) (both P<0.05 vs TH-treated WT mice). Inhaled nitric oxide during TH (n=7) prevented brain injury compared to TH alone (n=7) without affecting cerebral blood flow after CA/CPR (n=6). Conclusions NOS3 is required for the beneficial effects of TH. Inhaled nitric oxide during TH remains beneficial and further improves outcomes after CA/CPR. Nitric oxide breathing exerts protective effects after CA/CPR even when TH is ineffective due to impaired endogenous nitric oxide production.

Cognitive and Functional Consequence of Cardiac Arrest

“…Nimodipine did not improve neuropsychological or cognitive functioning in 68 cardiac arrest patients in a 1993 study [52]. Medical gases, including nitric oxide, hydrogen sulfide, and hyperbaric oxygen, are being considered for neuroprotection as well, and nitric oxide has shown some benefit in mouse studies [76,77]. A recent randomized clinical trial of 110 comatose patients with OHCA found that inhaled xenon combined with hypothermia compared to hypothermia alone resulted in less white matter damage as measured by fractional anisotropy of diffusion tensor MRI but did not result in a statistically significant improvement in neurological outcomes or mortality at 6 months [78••].…”

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“…7,8 This directly impacts the required chest compression rate in those species as mice should undergo ≈400 compressions per min to be resuscitated. [9][10][11][12][13][14] Magnetic resonance imaging also showed that usual ejection fraction are higher in mice as compared to humans (75% vs 55%). 15 Due to their very small body size, the ratio between the left ventricle and the body weight is also much higher in mice than in humans.…”

“…They are based on the clinical evaluation of consciousness, behavior, breathing, reflexes, and locomotion tests. 9,[11][12][13][28][29][30][31]41,50,53 Neurological recovery can be further assessed with quantitative behavioral tests in rodents, such as the T maze or the Morris maze test. [59][60][61] In addition to the clinical evaluation of neurological function, histopathological damages are also usually evaluated in most experimental studies.…”

How Can we Study Cardiopulmonary Resuscitation and Cardiac Arrest in Animals: a Review

“…On the other hand, spontaneous heart rate is much higher in rodents than in large animals and humans as usual values average 260-450 or 500-600 beats per minute in awake rats and mice, respectively [7,8]. This directly impacts the required chest compression rate in those species as mice should undergo ≈400 compressions per min to be resuscitated [9][10][11][12][13][14]. Magnetic resonance imaging also showed that usual ejection fraction are higher in mice as compared to humans (75% vs 55%) [15].…”

“…In survivors, neurological function is typically assessed using clinical deficit scores with specific grids for each species. They are based on the clinical evaluation of consciousness, behavior, breathing, reflexes, and locomotion tests [9,[11][12][13][28][29][30][31]41,50,53]. Neurological recovery can be further assessed with quantitative behavioral tests in rodents, such as the T maze or the Morris maze test [59][60][61].…”