Implantable real-time oximeter to determine potential strokes and post-traumatic brain-injury complications

Abstract

A first embodiment of the implantable real-time oximeter of the present invention is attached around a blood vessel near the site of a likely stroke to monitor large and medium size cerebral arteries. Another embodiment of the implantable real-time oximeter can be passed within cerebral blood vessels to monitor the oxygenation status of the surrounding cerebral tissues. When used within cerebral blood vessels, the emitter and detector are coplanar and contained in a small area, for example, 50-120 m.

Claims

1. An implantable extravascular pulse oximetry probe comprising: a red light emitter and an infrared light emitter configured in a semicircular shape and electrically coupled to an emitter driver circuit; a photo receiving sensor configured in a semicircular shape and optically coupled via fiber optics to a photo diode; the photo diode providing an electrical signal indicative of blood oxygen saturation values and pulse distention values; an attachment configured as a cylindrically shaped tube having a longitudinal opening for cylindrically attaching the red light emitter and the infrared light emitter and the photo receiving sensor around a blood vessel such that the attachment embraces the blood vessel and a transmission optical path is created through the blood vessel from the light emitters to the photo receiving sensor once implanted and placed on the blood vessel.

2. The probe of claim 1, further comprising cushions for separating the emitter from the detector.

3. The probe of claim 1, further comprising a covering around the red light emitter and the infrared light emitter and the photo receiving sensor.

4. The probe of claim 3, further comprising a hook attached to the cover for suturing the probe to tissue.

5. The probe of claim 1, wherein the red light emitter and the infrared light emitter and the photo receiving sensor are concave.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred embodiments will be set forth in detail with reference to the drawings, in which:

(2) FIG. 1 is a diagram showing the basic circuitry of the oximeter according to a first preferred embodiment;

(3) FIGS. 2A and 2B are diagrams showing cross-sectional views of the oximeter probe according to the first preferred embodiment;

(4) FIG. 3 is a diagram showing the manner in which the oximeter probe according to the first preferred embodiment surrounds the blood vessel;

(5) FIG. 4 depicts the emitter and sensor in an un-assembled state;

(6) FIG. 5 depicts the emitter and sensor in an assembled state in a variation of the first preferred embodiment;

(7) FIG. 6 depicts the probe of FIG. 5 attached to a blood vessel;

(8) FIGS. 7A and 7B are diagrams showing the probe according to a second preferred embodiment;

(9) FIG. 8 is a diagram showing a fiber optic sensor pathway for use with the probe of FIGS. 7A and 7B;

(10) FIG. 9 is a diagram showing four probes according to the second preferred embodiment within a lumen of a blood vessel; and

(11) FIG. 10 is a screen image of device outputs.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(12) Preferred embodiments of the invention will now be set forth in detail with reference to the drawings, in which like reference numerals refer to like elements throughout.

(13) FIGS. 1-6 show the first preferred embodiment, known as oximeter A.

(14) FIG. 1 shows the basic circuitry of the extravascular oximeter 100. The oximeter 100 includes a light emitter 102, silicone cushions 104, and a photo receiving sensor 106 configured in a cylindrical shape to surround a vessel (not shown in FIG. 1). The emitter 102 operates under the control of an emitter driver 108 to emit light at two wavelengths, e.g., in the red and infrared ranges. An output of the photo receiving sensor 106 is made incident via fiber optics onto a photo diode 110, whose output signal goes to amplification and filtering circuitry 112 and recording circuitry 114.

(15) FIGS. 2A and 2B show the oximeter A cross section. A waterproof semicircular light emitter 102 and a light sensor 106 are provided. An outer covering 116 will embrace both the emitter and the sensor to keep them in place and protect them from moisture. Nylon hooks 118 will receive sutures, which will be used to attach the assembly to the body wall. The sensor will be tested initially while it is embracing the aorta as well as the inferior vena cava of 400-600 g Sprague Dawley rats.

(16) FIG. 3 shows the sensor 100 wrapped around an aorta or inferior vena cava A.

(17) FIG. 4 shows the emitter 102 and the sensor 106 in an un-assembled state.

(18) As shown in FIG. 5, the emitter 102 and the sensor 106 can be attached to a plastic tube 120, in which case the silicone cushions 104 are unnecessary. The plastic tube 120 has an opening 122 so that it can be clipped onto a blood vessel A, as shown in FIG. 6.

(19) The emitter 102 has the ability to adjust to the light level automatically. Various intensities of light can be used, depending on the environment.

(20) FIGS. 7A-9 depict a second preferred embodiment-oximeter B.

(21) FIGS. 7A and 7B show the second preferred embodiment, namely, the intravascular pulse oximeter (B) 200. The diameter of the sensor 200 will be in the range of 600 m at the initial stage. At the final stages, the aim is to miniaturize its size to approximately 50 m. This is feasible, as there are 125 m fiber-optic oxygen sensors commercially available in the $100-300 range. With oximeter B, the light emitter 202 and the receptor 206 will be in the same plane. A rubber sleeve 216 will encase them both. A touch sensor 226 in the periphery will register sensor contact with the vessel wall. Biodegradable fibrin glue will be applied to the rubber sleeve, which will allow the sensor to be chronically placed. A ball and socket joint 228 allows the oximeter 200 to adhere to the vessel contour while providing a connection to a connecting cable 230.

(22) FIG. 8 shows the basic fiber optic sensor pathway that will be used to record during phase 2 of the project. It was excerpted from Hickey, M et al., Journal of Clinical monitoring and computing (2011) 25:245-255; while it was not originally designed for an oximeter according to the present invention, it can be adapted for the oximeter B 200. An emitter driver 208 controls a red emitter 232 and an infrared emitter 234 to emit red and infrared light, respectively. Their outputs are combined by a Y piece 236 and input via a single transmitting fiber 238 into the oximeter 200. Light from the sensed area goes through a single receiving fiber 240 into a photodiode 210, whose output goes to a 1V amplifier 242 and a demux 244. The above components communicate via isolation 246 with filtering and amplifying circuitry 248 and a computing device 250. Similar circuitry can also be used for the oximeter A 100 of the first preferred embodiment.

(23) FIG. 9 shows four oximeters (B) 200 in action within a lumen L of a cerebral vessel V. Each sensor 200 obtains readings from tissues around the periphery of the blood vessel in an area of measurement M. This will allow for isolation of the area of ischemia. A few sensors can likewise be arranged to monitor a larger brain area, as shown in the figure.

(24) The oximeter can be incorporated into a MERCI catheter or a Penumbra catheter to evacuate the thrombus at the same time. A common transmission line 252 is used. The output of the sensor is sent to a computing device to analyze the output to achieve any of the above ends. The computing device will be programmed with a suitable algorithm. The device will measure real time oximetry, heart rate, breath rate, breath distension and pulse pressure. Since the sensor and the light emitter are directly attached to a major blood vessel, the measurements will be very accurate and should not have artifacts such as those that are common in the above skin versions of oximetry presently used in clinical settings.

(25) FIG. 10 depicts a screen image of devie outputs.

(26) The physiological parameters measured and their scientific basis are as follows. The oximeter provides real-time percent oxygen saturation of functional arterial hemoglobin.

(27) Real-time cardiac pulse rate is given in bpm (beats per minute).

(28) A real-time breath rate measurement is updated every few seconds. Note that this parameter is derived from respiratory effort, not airflow, and will be present even if the patient is experiencing an obstructive apnea, as long as breathing effort is present. Breath rate is given in breaths per minute or brpm.

(29) Pulse distention is a measurement of the change in distention of the arterial blood vessels residing between the sensor pads due to a cardiac output pulse. It is a direct measurement of changes in local blood volume that accompany each cardiac pulse. Since the preferred embodiment records from the aorta, the readings are very accurate. For a given vascular compliance, pulse distention can also provide a surrogate for pulse pressure.

(30) Pulse oximetry measures the oxygen content of arterial blood. The blood is identified as being arterial because of its pulsatile nature. That pulsation is identifiable because it causes a cyclic change in the absorption of light energy from the red and infrared LEDs (Light Emitting Diodes) as it passes through the vessel, due to the presence of changing quantities of blood that occur with every heart beat. Because the blood is arterial, it possesses systemic arterial oxygen content, which is measured. Pulse distention is simply a measurement of the change in the effective path length of the light that passes through only the arterial or pulsating blood, and it has true linear distance units of m.

(31) One could envision this by theoretically placing all of the arterial blood residing in the light path between the sensor pads into a cylinder that has a cross-sectional area equal to the cross-sectional area of the column of the light beam passing from the LEDs to the photodiode. If the cylinder had one inlet and one outlet for the blood to enter and exit, then the level of blood in the cylindrical chamber would rise with each cardiac ejection stroke, and lower during each subsequent cardiac filling phase. The change in height of the blood in that cylinder between ejection and filling, or systole and diastole (Systolic BP-Diastolic BP), would then be measured directly as pulse distention.

(32) The larger the pulse distention value, the more arterial blood will be available to make oximetry, as well as heart rate and breath rate, measurements.

(33) Breath distention is a measurement of the change in distention of the arterial blood vessel residing between the sensor pads due to breathing effort. For a given vascular compliance, the breath distention provides a surrogate for intrapleural pressure.

(34) While two preferred embodiments have been set forth above, those skilled in the art who have reviewed the present disclosure will readily appreciate that other embodiments can be realized within the scope of the invention. For example, recitations of numerical values, specific technologies, and specific materials are to be considered illustrative rather than limiting.