Community health worker-based hearing screening on a mobile platform: A scalable protocol piloted in Haiti

OBJECTIVE

To establish the feasibility of a systematic, community health worker (CHW)-based hearing screening program that gathers Health Insurance Portability and Accountability Act-compliant electronic data (otoscopic images of tympanic membrane and audiometric evaluation) on a smartphone in an effort to streamline treatment options in resource-limited communities.

METHODS

This is a cross-sectional study in which four schools were screened in Port-au-Prince, Haiti, during in April 2018. A total of 122 subjects (61% female) aged 5-17 years underwent an initial brief audiometric screen followed by a more comprehensive air conduction audiometric evaluation if they failed their initial screen. Participants with more than 35-dB loss in any frequency on their comprehensive audiometric evaluation received endoscopic otoscopy.

RESULTS

Seventy-five percent of subjects (91/122) passed their initial screen. Of those who failed, 9% (4/44 ears) had a severe or profound hearing loss on comprehensive evaluation. Abnormal otoscopic findings (11/36 ears, 31%) included are cerumen impaction (n = 6), myringosclerosis (n = 3), tympanic membrane perforation (n = 1), and tympanic membrane retraction (n = 1). The average duration of the initial testing was 100 seconds (SD = 74 seconds), whereas the duration of comprehensive testing was 394 seconds (SD = 175 seconds). Extrapolating from these data, we estimate that a group of seven trained CHWs could gather formal audiologic and otologic data points for 100 children per hour using this protocol.

CONCLUSIONS

A systematic approach that utilizes local resources (CHWs) and existing infrastructure (cell phones and the Internet) can significantly reduce the burden of hearing healthcare specialists while simultaneously facilitating early diagnosis and management of disabling hearing loss in low-resourced settings.

LEVEL OF EVIDENCE

Level 4.

[Brain vulnerability and its modulation]

Clinical and experimental studies revealed that the injured brain is highly vulnerable to a subsequent insult. Surfery of the literature pertinent to clinical and experimental traumatic brain injury (TBI) is made. Increased vulnerability of the traumatically injured brain to an additional sub lethal ischemic, hypoxic, excitotoxic, or mechanical insult has been clearly demonstrated. Compared to traumatic brain injury alone, the double insult paradigm dramatically increases the brain damage. Brain vulnerability following TBI can be explained by a reduced ability to compensate for a reduction of cerebral blood flow (CBF) and oxygen (O(2)) delivery to the brain or inability to meet an increased metabolic demand. In addition, there is a specific increased sensitivity to delayed insults induced by the first injury. Potential mechanisms of the increased sensitivity to a second insult might be related to post-traumatic gene expression alterations leading to changes in neurotransmitters release, density of receptors and reduced thresholds for activation of pathways leading to delayed cell death. The brain is vulnerable to repetitive injuries. Derangements of compensatory mechanisms are responsible, in part, for this vulnerability. Additional work is needed to better understand the molecular pathways leading to secondary damage and to find novel therapeutic strategies to modulate the brain response to TBI.

Effects of hyperoxia on brain tissue oxygen tension in cerebral focal lesions

We evaluated the systemic and cerebral effects induced by an increase to 100% of the inspired oxygen fraction (FiO2) on 20 comatose patients with head injury (9 patients) and SAH (11 patients). Brain tissue oxygen tension (PtiO2) was measured through a Clark electrode inserted in penumbra-like areas. We performed 55 hyperoxia tests by increasing FiO2 from 35 +/- 8% to 100% in one second and calculating the PtiO2 index as: PtiO2 variation from baseline at 1 minute/arterial oxygen tension (PaO2) variation from baseline at 1 minute x 100. One hundred percent FiO2 caused an increase of both arterial (from 139 +/- 28 to 396 +/- 77 mmHg) and cerebral (from 22.6 +/- 14 to 65.4 +/- 60 mmHg) oxygenation after 1 minute. The range of the PtiO2 response was not uniform and two groups were identified. The change was small, 0.8 mmHg/min/100 mmHg PaO2 (+/- 0.7; range 0-2) when mean PtiO2 was 19.7 +/- 13.1 mmHg, while a stronger response, 8 mmHg/min/100 mmHg PaO2 (+/- 5; range 3-18) (p < 0.01) was found when mean PtiO2 was 31.7 +/- 14.3 mmHg. Since O2 diffusion should follow the gas diffusion law, the increase in diffusion distance due to a reduction of capillary density in focal lesions may explain this relationship.

Oxygen delivery and oxygen tension in cerebral tissue during global cerebral ischaemia: a swine model

Interest in tissue oxygen (PtiO2) monitoring is increasing. However the exact interactions between ptiO2, systemic and cerebral variables are a matter of debate. Particularly, the relationship between ptiO2, cerebral oxygen supply and consumption needs to be clarified. We designed a model to achieve progressive Cerebral Blood Flow (CBF) reduction through 3 steps: 1. baseline, 2. CBF between 50-60% of the baseline, 3. CBF < 30% of the baseline. In 7 pigs, under general anaesthesia, Cerebral Perfusion Pressure (CPP) and CBF were reduced through the infusion of saline in a lateral ventricle. PtiO2 and CBF were monitored respectively through a Clark electrode (Licox, GMS) and laser doppler (Peri-Flux). Blood from superior sagittal sinus and from an arterial line was simultaneously drawn to calculate the artero-venous difference of oxygen (AVDO2). Brain oxygen supply was calculated by multiplying relative CBF change and arterial oxygen content. PtiO2 reflected CBF reductions, as it was 27.95 (+/- 10.15) mmHg during the first stage of intact CBF, declined to 14.77 (+/- 3.58) mmHg during the first CBF reduction, declined to 3.45 (+/- 2.89) mmHg during the second CBF reduction and finally fell to 0 mmHg when CBF was completely abolished. CBF changes were also followed by a decline in O2 supply and a parallel increase in AVDO2.

CONCLUSION

This model allows stable and reproducible steps of progressive CBF reduction in which ptiO2 changes can be studied together with oxygen supply and consumption.

The lipid peroxidation by-product 4-hydroxynonenal is toxic to axons and oligodendrocytes

Lipid peroxidation and the cytotoxic by-product 4-hydroxynonenal (4-HNE) have been implicated in neuronal perikaryal damage. This study sought to determine whether 4-HNE was involved in white matter damage in vivo and in vitro. Immunohistochemical studies detected an increase in cellular and axonal 4-HNE within the ischemic region in the rat after a 24-hour period of permanent middle cerebral artery occlusion. Exogenous 4-HNE (3.2 nmol) was stereotaxically injected into the subcortical white matter of rats that were killed 24 hours later. Damaged axons detected by accumulation of beta-amyloid precursor protein (beta-APP) were observed transversing medially and laterally away from the injection site after intracerebral injection of 4-HNE. In contrast, in the vehicle-treated animals, axonal damage was restricted to an area immediately surrounding the injection site. Exogenous 4-HNE produced oligodendrocyte cell death in culture in a time-dependent and a concentration-dependent manner. After 4 hours, the highest concentration of 4-HNE (50 micromol/L) produced 100% oligodendrocyte cell death. Data indicate that lipid peroxidation and production of 4-HNE occurs in white matter after cerebral ischemia and the lipid peroxidation by-product 4-HNE is toxic to axons and oligodendrocytes.

Quantitative assessment of ischemic pathology in axons, oligodendrocytes, and neurons: attenuation of damage after transient ischemia

Axons and oligodendrocytes are vulnerable to cerebral ischemia. The absence of quantitative methods for assessment of white matter pathology in ischemia has precluded in vivo evaluation of therapeutic interventions directed at axons and oligodendrocytes. The authors demonstrate here that the quantitative extent of white matter pathology was reduced by restoration of cerebral blood flow after 2 hours of middle cerebral artery occlusion. Focal ischemia was induced in anesthetized rats by intraluminal thread placement, either transiently (for 2 hours) or permanently. At 24 hours after induction of ischemia, axonal damage was determined by amyloid precursor protein (APP) immunohistochemistry, and the ischemic insult to oligodendrocytes was assessed by Tau-1 immunostaining in the same sections. In adjacent sections, ischemic damage to neuronal perikarya was defined histologically. The hemispheric extent of axonal damage was reduced by 70% in the transiently occluded animals from that in permanently occluded animals. The volumes of oligodendrocyte pathology and of neuronal perikaryal damage were reduced by 62% and 58%, respectively, in the transiently occluded animals. These results demonstrate that this methodologic approach for assessing ischemic damage in axons and oligodendrocytes can detect relative alterations in gray and white matter pathology with intervention strategies.

[Monitoring and protection of the central nervous system in subarachnoid hemorrhage during intensive care]

Subarachnoid hemorrhage has cerebral and systemic consequences as well. The main purpose of admitting a patient in the Intensive Care setting is to provide protection, mainly by stabilizing fundamental physiological parameters. There are both systemic parameters and cerebral parameters to be controlled continuously, and cerebral parameters may consider the brain as a whole (global cerebral parameters as intracranial pressure) or may provide information on specific areas. Cerebral protection may be achieved only when multiparametric monitoring is instituted, since only the combination of many physiologic parameters provides information capable of identifying, and hopefully of treating, deleterious derangements.